thanks for all your support again x
It just goes on and on this situation and the latest has confirmed to me that ExP must be deluded because I think he actually needs someone to explain to him where he's in the wrong.
DS was much better on Monday and via text I agreed albeit reluctantly to contact as usual on Tuesday. ExP texted back that he'd come and pick DS up at 11. I pointed out that 11 was a little late and it was his usual contact day, so I'd already made plans (solicitor appt) and he would need to come earlier or later (and later would not leave much of day left).
He phoned my home phone and left a message, as I didn't answer the phone, saying he was coming at 11 and I'd better be there. He phoned a further three or four times very aggresively telling me I was denying him contact with his son if I wasn't there at 11, that I'd lied about DS being ill because I didn't want him to see DS, that I should be ashamed of myself as a mother, that my son would be very proud of me in the future, that they (he and NP) had a lawyer and they could pay - he was nearly wetting himself with delight in telling me that part. He said, without any hint of doubt in his voice that "he can do anything"! He truly feels invincible with "his" newly accquired wealth.
And the best thing....I laughed at these messages...because they were soooooooo ridiculous.
DS could hear his aggression too though. 
Then he phoned back and said "take DS to my mum early in the morning" and I quickly picked up phone to tell him that I wouldn't be doing that either.
An hour later his NP calls my mobile asking reasonably on his behalf, what was happening with pick-up in morning. I explained situation, and she offered to pick-up DS at 9am to which I agreed (although later I felt really, really uncomfortable with that decision). Lo and behold ExP turns up at 9am to collect DS.
Solicitor is working on draft in response to his ridiculous letter and stating in no uncertain terms that his behaviour is unaaceptable and must stop.
I don't know what he is ultimately pushing for to be honest. The solicitors letter he sent states he wants joint residence which I'm pretty sure he thinks means 50/50 - not workable in this case, not good for DS, and, as my solicitor assures me, not likely. I just hope she's right.
Most importantly, DS is well, with me, and it's peaceful ATM.