Need help with imessage and someone else getting my texts.

Yesterday i bought a phone, NOT A IPHONE, a samsung. And i got a brand new number. The number i got belonged to someone else before they changed theyre phone, the Person has an iphone but changed their number. They CHANGED their number, but for some reason they are receiving MY TEXTS (only from my friends with iphones/imessage

) i was able to get a hold of him and i told him to just turn off his imessage. I read online about that youre supposed to turn off imessage and reset network settings etc. but i did not know at the time i am worried he will sign back into his apple id and get my messages again, or because he turned off imessage and put it back on while my NOW number be erased from his phone? thanks.