absa adjust installment without consultation with me

Absa adjusted my installment downwards without my permission simply because I paid more money than was my monthly installment. The reason for paying more was so that I don't have to pay for certain months. The amount paid was therefore supposed to cover the months I would not be paying. Now I have to pay again next month whereas the idea was to pay for those months. Shouldn't absa have communicated with me first on what where my intentions?