Poor service on unallocated payments months later

im so sick and tired of SBSA and their nonsense. I have called, sent emails and still no feedback, A payment was made on the 20th of October and almost 3 months later the payment hasnt been allocated on my account and im being charged interest still. This is costing me time and money, phoning and holding on for over 30min just to get through to a consultant who only tells me about alpha accounts.