Louise, firstly, I want to say, I admire you 100% for sticking to what your son wants. I was such a child in the 60's, unfortunately my Mum, like most women in those days, had no rights whatsoever! Even if I were ill, my Father insisted in taking me out - if my Mum refused, he hauled her into Court, were the Judge - mostly a MAN of course, would give her a right going over! So fair play to you Louise, for sticking by your sons wishes.
Bringing it into the 21st century, I would suggest that you plead with your son, to let his father see him, in the presence of a Social Worker or someone who is trained in this sort of issue. Try and convince the lad to be brave enough to tell his Dad what his views are and that he is the one who does not want any contact with him and keep the interview as short as that.
Worst case scenario? The father will haul up in front of a Magistrate, whom, in this day and age have a lot more savvy that 50 years ago! The thing is, kids DO have a voice and a say in these matters now if they go that far.
I applaud you Louise, and admire the fact that you are there for your little lad, and I really do hope that it will all work out for the best. Bless! ♥