Cell C debiting me on wrong dates and debiting my twice

I am appalled by cell c's service. Absolutely disappointed with this firm

Firstly debiting my account on the wrong date monthly. Snd now debiting me more than once when my account is up to date.

They have ruined my credit score. How do I give them back their phone to cancel this account because I am fed up of wasting my airtime and calling every month to speak to *********** people