please cancel as i did not request for downgrade i want all recordings proving who agreed to the downgrading

i took out a contract it ended last year November, their call centre called me for upgrade i told them i am not upgrading, they are still billing me and i called this week to query i was told i took a downgrade of R175 of which i did not do that is *****, can you please investigate and cancel the contract a my contract was for t 24 months and i did not request for extension, i kept on reversing the debit orders which affects my credit score very negatively , they are refusing t cancel the contract why, i did not request for downgrade