No allocation of my payment since December 2015

i went to pay my account in December 2015 and I was advised by the cashier that my payment will reflect the next day, I trusted them they will keep to their promise. I received a call in mid January 2016 advising me that I have not made payment to my account, I was shocked to learn such a thing since I remembered well on the 18th of December I made my payment due on my account. I told the agent who called me I had proof that I made a payment back in December 2015 on the 18th, so I decided to go to the store EDGARS Active in Clearwater mall where I made my payment and all they did was to give me my slip confirming my payment and this was still not allocated, so frustrated as I was I made another payment and closed off my account immediately and asked for my refund for the cash payment made in December 2015. i was told by the cashier to email or fax my proof of payment to the head office so i can be refunded my payment and i did so. the following day i called the head office asking about my refund but they said to go back to the store i made the payment, all off this was happening with me wasting my airtime and my petrol for a simple transaction inquiry. all i need is my refund