Incorrect Installment

Last month I paid a large amount of money into my account. The amount would have been equivalent to about 9 monthly instalments overall. I then received my statement with the exact same instalment as the previous month! When I queried this with the call centre I was advised Mr Price have been experiencing numerous problems with statements-this is not my problem. My instalment was suddenly halved, however when I went into the store to pay nothing had been corrected on the system! This was a huge inconvenience! My total due this month should actually be ZERO due to the large amount I paid last month. I should not be expected to pay anything at all! Please check your records and amend my statement. I am very angry with the whole situation and clearly the accounts department are not calculating their figures correctly! I am very frustrated as I shouldn't have to be spending so much time trying to resolve your error.