unauthorized December debit orders

So I have 3 funeral policies with Assupol and an sms was received about a week ago informing me that they MAY debit my account on the 14th of December which is not my pay day mind you.they never bothered to phone me and ask if it will be okay for the debit to go off. this morning I noticed that they have debited my account and I phoned and spoke to Arabetswe who told me that it was a management decision to run the debits. I have left funds in my account for a debit order that goes off my account on the 15th of every month which will run tonight but there isnt enough funds anymore because of the bad services from you guys. this will cost me bank charges and give me a bad name. I dont owe you Assupol a cent for December and you have no right whatsoever to debit me whenever you feel like. I want that money reversed ASAP so that my tonight's debit order can be accommodated