wont acknowledge my cancellation/ termination of contract

I have cancelled my contract as it was a month to month home router.

I returned the router to the shop and paid my account ensuring its up to date. I was told that it was cancelled and all is fine.

I have been invoiced and debited of which I do not understand why.

I went to the shop at Ferndale on republic and the consultant told me it was still open and active ? why would such happen as I cancelled everything ?

this reflects bad and affects my credit score Do resolve this !!!!!!!!!!