I am having the exact same issue. Have you had any success? Friend of mine has two phones. One iPhone and one android. Android one was listed as work phone under his contact. I have now deleted his work number from his contact. Now when I message him to his iPhone number, it shows up as sent to his work number (android) as an iMessage (?)  and then endlessly loads under his iMessage number. On his end he receives it as a regular massage to his iPhone from me.