Billing for a return item for almost a year

Very disappointed with the service i received. I bought a tablet which was delivered to me, i was unhappy and return the tablet , the guy that collected it said all is in order i have witnesses that saw him take the tablet last year 2017. I get a call that my account has been handed over to the lawyers. I was shocked because i do not have a vodacom account then after investigating it was the tablet that i return that i been apparently billed for over this pass year. I have filled in affidavits and sent it through, i have even ask if vodacom can review their calls as proof that the tablet was sent through but i have received no satisfaction. I refuse to pay for an item that i sent back fully packaged within the 7 day return policy. I feel this is unfair service.