Miisallocation of payment

Worse service ever and their staff members are like robots and not willing to assist. I paid my account on the 22 December for the 25th since it was Christmas Day and it was not allocated to the instalment. It was allocated as it suits them and I have been told my account is in arrears. I have paid more than the instalment and I am receiving messages for no payment and legal hand over while they are sitting with almost triple the instalment payment. Tried to chat to them and 2 queries have been logged but till today my account payment is not allocated properly and I am been asked to pay more.