Getting charged for BYOD Smart Watch line after cancellation

I cancelled my Smart Watch line back in December 2019, since then I am still getting charged $10 for this line I don’t even use. I keep talking to agents and they assure me that they will take care of it but it never happens, I spent 2 hr already speaking to them.

What should I do? Looks to me that they are not able to deactivate the line.