Early Debit

I have an Insurance Policy with African Bank, and have just noticed that they debited my account early for the current month. Who gave you the mandate to do so because even on your Payment Instruction / Authorisation, it's clearly stated that my Account will be debited on the set out date (21st of each month), or after, why are you breaching the Contract that you drafted? Is this allowed? I expect a detailed response from you which makes sense, your failure to respond will result in me breaching your very own contract by reversing all the debits that went thorugh in the past and cancel the policy. If you can breach your very own contract, then what's stopping me from breaching it also??