Unhappy customer

Vodacom just called me following my review and they say they cannot help me. That at some point i made a cash payment towards the account i am querying and i did not make any cash payment. I am being listed for a number i am not even using and have not used in years. they say there are records of me calling and cancelling my contract and that i should provide proof, where will i get proof of the call from 2015. they say without this, they cannot help me.