instalment higher than required as agreed

good day I have a credit card with Standard bank last month I paid R17000.00, to settle my budget transactions on the 19 of April and I called in to advice them to settled the budget account so that my instalment to be lesser only to find out that it was not done, when I call on the 20th of April they informed me that my payment will be allocacted on Monday 23 of April (ref ********** 414) which they did not do, on the 09/05/2018 i checked my statement instalment is higher and amount was not allocated , i called in again i was inform that it was only done on the 7th of May instead of 19th of April and i laid a complain spoken to Johana Kele ref( ********** 352) she advice me that they will look at it and call me today for feedback which was not done , i called in again today she was busy on the line i was advice to leave my cell number so she can call back, she called back and advice me that complain has been refered to the department that took long to allocate the money.

i asked her the question what is going to happen cause next week my instalment is due and i don't have R2561 that i required this month as i though my instalment was going to be lesser in May ,she said am still liable for the instalment that is required May as the bank charges 3% of your transactions and when i calculate my balance the instalment that am supposed to pay this month is R776.98 my Total amount outstanding on this statement R25,899.41.

she told me that i need to make arrangement and inform the credit department that am unable to pay the whole amount required for May, which i wont do as this is not my fault its their fault.