Vodacom is a disgrace

I get my invoices every moth, and I have a set contact, but what they take from my debit order is a total different amount. My debit order is supposed to go off the 1st day of each month, the next day I get a call advising me that my account is in arrears, so my debit order did not go off on the 1st. I made payment, and then still they will take off my debit order. I reversed the debit order, so they just add money to my account. Vodacom is absolutely pathetic as well as the services, I will not pay more than what my invoice states. Vodacom is *****ing their customers money. I am very disgusted in them.