Abusive ex wants access

I have an urgent enquiry and would highly appreciate if you could please provide me with some guidance.

I have a son (X) who is 7. When he was 3 both I and he had to move into a woman's refuge. I was (and still am) married to his father and sponsored him to UK. His visa has now expired and he wants to use his parental responsibility as an excuse to stay in UK although he has not shown any interest in his son for past 4 years.

He recently contacted my family to ask them to ask me to get back with him or at least provide him with my passport details so he could renew his visa. I refused this and now by help from relatives he has heard another way of staying in the country would be using his parental responsibility. I have already reported his case to the UK border and they are looking at his case and have informed he may still stay in the country as the divorce has not gone through yet so we are still married.

I have received a letter today in terms of court order from his father for him to having access to X and also a prohibited steps order against myself. His father has obviously not told his lawyer anything about what he has been doing to X and me. He has instead said that I have abducted his child and denied access to his child. Truth is there was severe child protection issues in place at the time we lived together and my son's health visitor had advised me that if X was not removed from the environment (not with his father unless his father changed for the better) then X could be taken by social services.

Now I have to go to court in June and I am worried sick that I may be losing my child (not literally but by him having access it can do so much damage). I am a student and do not have any income apart from childcare benefit+childtax credits so I don't know if I can get legal help for free. I once saw a solicitor straight after the seperation and at that time my solicitor said although there has been child protection issues e.g. X's father sexually abusing small girls+severely neglected X then those are only verbalal allegations and not legal evidence so he still stands 50-50 chance to win the case. If some other parents here have gone through something similar they may be able to advice on how they prepared their child/children for all that?  Do you have any advice on how I can keep the case stronger? There are lot of things which happened however the problem is I never reported it to the police and there is nothing much to show as evidence. The only thing I can think of is to contact the health visitor but apart from that I don't know what to do. He has denied that he has ever been abusive. How can I prove this in court especially the psychological abuse?? He has stated that everything I have said is false allegations.

With regards to evidence this is all what I have:

In terms of my son, he has already told me he doesn't want to and why he doesn't want to but I am concerned whether my son's wish would not be taken into account as he is so young? After the seperation I asked the new health visitor if my son needed any psychological input or investigated if he has been sexually abused and she said he seemed to manage things well and seemed so much happier and that perhaps by receiving psy. input it could make more damage if he is coping ok. So he did not receive any psychological input however recently (approx 6 months) he has started to recall memories and broke down telling me about his father neglected him and was emotionally abusive to him (he does not recall any physical or sexual abuse). He has lot of negative memories though from the time he lived with his father  of how he treated him, but he cannot remember how he treated me apart from me being upset.

When I lived with him there was one incident which involved physical violence however there was an on-going psychological abuse where he was very controlling and isolated my son from being with him ect. Told my son that mum doesnt love him and that he shouldn't go near me ect. I never reported anything to the police. All I have reported is that he harrassed me with e-mails and phone calls after I left him so they gave him warnings and I did not hear from him after that.

With regards to the sexual abuse, these happened to girls who were around 10 years old and their family is aware of this but due to their cultural background they chose not to report it. This means he has never been on any register or legal system for this. The girl who was sexually abused by him has agreed to provide written statement or testify via video link. There are several family members (again abroad) who have admitted they knew of his pervert background. This was unknown to me until after the marriage.

The problem is that in the meeting with the health visitor she said she will inform social services and that they will take his laptop to investigate whether there was childporn ect. However everything happened so fast and once we moved out i contacted the social services to see if they have followed the case up but they said that because my son was no longer in danger and had been removed from the environment they have closed the case! So again, no evidence from the social services. Only health visitors notes.

Thank you so much for your time and help