Incorrect debit amounts

Since July 2021 Cellc has messed up my account with them they've been deducting incorrect amounts to my account when my debit orders go off I've logg a query numerous times still not sorted out every month I have to pay a penalty fee for reversing those incorrect debit amount this is pathetic no one in stores are helpful not even agent's over the phone when you call in I'm definitely ending my contract with them