Hearing Aids and the Phone

Ever since the last iPhone update my phone is not connecting with my hearing aid. All the other apps I've tried so far, are fine. It's just the phone. This is it making very difficult to have a conversation.

Can anyone tell me what I have done wrong? I want to be able to get the phone sound to go into my hearing aids as quickly as possible. Right now I'm having to use the speaker mode and I don't want everyone hearing my calls.

Thanks for any help you can give.