disconnected number issues still active

Listen to this issue that t-mobile cant resolve or have an answer to. I changed my phone number in april 2024 and it still rings to a voicemail in which i don't have access to. I was worried someone hacked that number. because when i first disconnected it, it had the disconnect message than all of a sudden, it started going to vm per friends and family trying to contact me via my old number by accident. so it has caused so many issues still having the voicemail active and i can not access that old voicemail since changing the number. So i called tmobile 3 times and they assure me its cancelled and can't explain why all of a sudden it goes straight to voicemail. This has been a security concern for me and tmobile isnt resolving it