As I explained in the earlier dispute against you, negative feedback isn't intented for your situation.
Furthermore, he didn't make any false claims - you were able to create accounts through his proxies. Accounts don't get locked for simply being created, and thus the IPs he provided aren't solely responsible for your accounts getting locked.
Of course you are able to voice your opinion, but considering the trade was completed, and the issues with the one non-working proxy was resolved, you can't leave negative feedback. At most you'd be able to leave a neutral.
As for not being notified - that was my fault. I felt like the first feedback didn't immediately deserve a warning point, considering it was obviously unclear when one is supposed to leave negative feedback. As such, I didn't issue a warning at all, which I should've done without any warning points attached.