Poor service from Accounts

The experience I had this past month in dealing with CellC has confirmed to me why they are going under and why I have decided to cancel my contract with them. From the 20th December till now they cannot allocate a payment made via their own app to my account resulting in me being charged double this month. The person who tried to assist me throughout the month has been going over and beyond to have the matter resolved and escalated to management and till today nothing has been done to rectify the matter after endless phone calls and mails sent with the proof of payment attached, they don’t bother to reply.