Conundrum to solve

Please could someone clarify? My debit order date is the 27th of every month. I have paid for January, February and March R4230 each month. On the 1st of April the rate went up to R4543 I have been told that I owe R4543 since the 1st of April.

The big question is: Why do I need to pay R4543 before the 27th of April?

I have been told in more than one email and two Whatsapp IM sessions that I owe this amount and therefore my account has been suspended.

Could anyone please explain to me why I need to pay before the 27th of April?

Thank you