OP, it may help people to read your post if it's put into an easier format, so here goes:
"My ex ran off with my son. It took a year and a half to get him back. We have two children though my ex ended up with a shared residency order.
"The same day it was awarded, I was due to have the kids (they live with me from mon to fri). My daughter had serious injuries that were investigated, and found to not to have happened the way he said it did.
"Social services stopped contact since no-one could offer an explanation of how it happened.
"Contact was resumed and again my girl came home with more severe injuries and the same thing happened. They said there was "no possible way that her injuries were inflicted" the way my ex said, but could not give an explanation, and so once again, contact resumed.
"Then my ex began calling social services about me daily, accusing me of awful things. Each time I've been investigated, social services have been satisfied with my parenting and closed the case.
"My ex then phoned Social Services and accused my partner of beating my kids and refused to send them home to me, claiming he was safeguarding them.
Yet again, I was investigated. He has done this a few time previously with another ex and two of my friends, and so there is a pattern, and now he has the kids once every few months.
"Bearing in mind he is meant to have them every weekend, I decided enough was enough, and with social services support, I stopped contact.
"Now, he has phoned the court and is pushing for me to be arrested and sentenced to prison or have the order enforced.
"I have plenty of evidence to back up what I have just written; the thing is I want to go back to court but cant afford it and according to him, as he put a facebook status up saying how he is going to have it enforced and saying that, as I am breaching the order, I have to pay to go back to court.
"I am very worried about my kids around him and surely, since he didn't maintain regular contact as agreed, he was the one in breach.
"I think a few months is a bit long to not see your kids, so surely he would have to pay and I should have the right to withdraw from the order if he breached it first.
"Please help me, I'm worried sick."
It's good that Social Services seem to be supporting you. I recommend that, rather than wait for your ex partner to apply to enforce the current order, you take the initiative and make an application to suspend or vary contact.
If you can not afford a solicitor you can obtain the forms from the HMCTS (court) service.
I can't remember whether it's a C1 or C2, as haven't done family for a long time.
If you can't afford the court fee, you can also apply for exemption from the fee, again the form is downloadable from the court website.
Hopefully one of the family lawyers will be along soon to help.