I had struggle to change my phone number in #telegram , but I made it:

I turned on my dual app and login in telegram with my phone number, so I after a SMS I was logged and saw the previous owner chats.

then I requested in the web to delete my account. and the chats disappear.

close the dual app and after a few mins open the one were I want to exchange the number. they sent me and SMS that automatically picked up. and done