Debit after contract has ended

So cellc decides to debit my account after my contract ended with them .....then I contact them and the agent has a nerve not to answer me and just went silent.....wht kind of customer service is that....then put me on a pinnacle400 whr I mus pay more money and for a year an a half I was on a epic 100 top up....I am not going to be held liable for the amount that was debited from my account im sorry