Ex refusing to sign sale contract

Long story as short as possible I divorced my ex last year. We have a financial order that states I was to keep the marital home, and pay him £50k. This had to be done within a few weeks of the Decree Absolute. If I couldn't pay then the house has to be sold and he would get his £50k and the rest to me with me paying all sale costs . I couldn't get a mortgage as my credit score is pants thanks to him. I have kept up with the mortgage payments with no help from him for 3 years, and the house was sold at a price he agreed on which was 30k more than the matrimonial valuation. The conveyancer sent the completion statement today as we are due to complete in 2 weeks but he has now said he wants to put the sale on hold and take me back to court as I will get double what he is due and he does not agree with that. I have complied with the court order in every way and we could lose this sale because he is not happy with his amount.... stated in the order! If we lose this sale this will impact on me massively financially as I am bearing all costs of this house by myself and have had to borrow money from family to do repairs to get it to a sellable condition. What can I do about this? I am not in a position to keep this house going and there is no reason to stop the sale other than him being upset that I am getting more than him. Incidentally I had a non molestation order due to coercive and controlling behaviour and this feels like he is trying to control me again!