I’m still having this issue on 12.1.2. It started a few months back and is driving me mad. I send a message to my mums phone number and it sends to their iPad. Sometimes it’s the other way around. The unpredictability of where the message will go just makes it worse.
My mums contact details on my iPhone only contains her phone number (no email address attached at all). The iPad and iPhone both use their iCloud address. My mums phone is set up to only send/receive iMessages from her phone number and the iPad is set to only send/receive iMessages from their Apple ID email address.
FaceTime works fine still - as in I can choose which device to call and it actually calls that device. The devices/accounts have been set up this way for years with no issues until iOS 12.
Ive even tried just typing the actual phone number number in the address box and sending a message that way but it’s still going to the iPad. When I open messages sent to to me from them, all messages are merged. It will initially show my mum as the contact in the top bar, but when I scroll so far up, the contact name changes to the iPad name. Deleting the message thread and seems to work temporarily, but the issue constantly comes back.
All devices invloved are using iOS 12.1.2
Any help would be greatly appreciated
Thanks.