A little update on the situation:

In the original post I stated that I am friends with his sister who backed my corner on a lot of what went wrong pre and post break up. I understand that he’s still her brother but she stated that she still wanted to maintain a friendship with me despite what had happened and we’ve kept in contact since.
Since he has some important items of mine, I was counting on his sister to return them to me, which she said she would. However, I can now see she has blocked me on WhatsApp despite us only having spoken on there on Friday (talking about how we should meet up soon!). I have text her since asking how she is and the message delivered but I have not received a reply.
There was no animosity between us and I can’t understand why she would just block me out of the blue, especially when my items are yet to be returned. I would have expected at least a text explaining why? Not just a random block and no contact, as I suspect her brother has asked her to maintain no contact with me…but what about my things?
What do you suggest I do?