Think carefully about contract with Cell C

On 17 April I've cancelled my mom's contract at the local store. Then on 15 May I realized the amount was still deducted from her bank account. I've sent customer services an e-mail and was told they will solve the matter. Today I realized on 15 June they have deducted even a bigger amount from her account. It seems once you have signed a contract with Cell C you CAN NEVER GET RID OF THEM AGAIN.