I've opened up a home Internet with them 2months back,all of a sudden they suspended my contract

I've opened up a home Internet with them 2months back,all of a sudden they suspended my contract.when I contact them they saying I'm owing them I really don't understand why because it is a debit order.it is not my fault they did not deduct as I have told them when to deduct,they missed a date and claimed that they did not find money into my account.why did they wait 3 weeks before they can suspend my service also how would I have know if I did not call.I don't want to lie I'm so disappointed in them,the treatment Im getting is not the same one I received when they wanted me on board.