Nimble pathetic service and unprofessionalism

The worst most annoying institution very unprofessional This people have been calling me about a cell c account that was paid off a year ago even after I sent the paid up letter till this day I am still getting 3/5 calls a day asking me to pay off a badly cell c account

It’s annoying what makes it even worse is the fact that even a year ago when I paid it off it was through them now how is it that the same company is still calling me about the same account