Mts — Bill paid but again some person call for amount

Dear sir, i am used 3 years back dongle no - [protected], i am informed that to customer care for cancellation in that time it's self because cheting in speed & network issue. After cancellation also billed 2 months, customer care persons call me continually for bill payment. I am not accepted to pay because i am not used,

After one year sent legal notice to me. As normal person i paid full amount i don't want face further problems.

After one year some call me for you pay bill amount. I tell to him i already paid. After 6 months some call & he tell to me you paid bill amount but you have pay charge.