Account paid off but keep getting calls

I'm still trying to sort out a problem ive been having with netstar since 2019 its tirjnh really... fast forward i got a revised and correct statement in March last year and I paid if off by October due to the fact that I was unemployed due to covid, but now all off a sudden I owe credit works R400+ and im tryjng to get in contact with someone in the retention department however cant get through.