Unreasonable billing from Mangaung Municipality

First of all the billing of my water account is sometimes unreasonable and today i called the customer service to enquire about the huge amount that they say i owe. I then called the customer care line and the gentle man that was assisting me told me that the last payment that reflects on their system was in July and which is not true. I then told him that besides making payments at the municipality i make them at Pep store or the Post office which is where i was advised to make payments at if i don't pay at the municipality by one of the colleagues at the municipality. So today i was told by the guy who was assisting me at the customer service that they usually struggle to get the payment when is made via Pep store or Post office and that i must get proof of payments in order to object the huge amount of bill i received from them which might be a problem for me since i always destroy my receipts with the intention that i have made the payment. So it seems i will have to pay that huge amount if i don't get proof from pep store.