Android STILL not receiving texts from Iphone even after de-registering.

My husband switched from iPhone to android.

1) The iphone was destroyed (so any solutions involving that will not work).

2) He DID deregister his number using Apple's tool.

He is still not receiving texts from iPhone users, and is missing important text messages. In addition, whenever a group message involves even 1 iPhone user, he also receives no texts.

I have searched the internet and have found no solution. T-mobile, his service provider says they cant help him either.

What can we do?

Thanks!