How are blocked numbers able to get through enhanced messaging

[Ninni565]

I blocked my ex from texting me on my sprint network but he can now use his old phone number to text me text me through enhanced messaging. I blocked his old phone number too, but his text still come through using enhanced messaging. How is that possible? How can his messages come through using enhanced messaging and how is he able to use his old phone number?
Does anyone know? Has this happened to anyone else?

 

[notional]

It's happening to me too. Your ex won't stop texting me either.