Telkom contract a nightmare

I had a contract with Telkom that ended in 2016, they called me in 2018 and told me i owe them about R2500 for my contract. I went to a Telkom branch and when i gave them my ID they said they cannot pick up anything on their system yet i still continue to receive calls where i am being told i owe Telkom. This is messing up my credit record and i want that resolved as it does not make sense that their system cannot pick up anything under my ID number yet i am getting calls saying i owe them and Telkom appears on my credit report.