Billing despite returned equipment and cancelled service

I returned my equipment in store almost a month ago. I was told my service was cancelled, but I was still charged.  I then called and cancelled my service again. I then was sent another bill a few days ago. I was also called and informed the my equipment needed to be returned despite me returning it in store. I was not given a receipt in store and as told I didn’t have to do anything else. I am not sure how to resolve this as the store doesn’t have a phone number and all of my other calls have not resolved the issue. I want my service cancelled, and I do not want to be charged for equipment I already returned.