Extremely Poor Service

I'm writing this pertaining to BP Garage Lakeside Proper . Yesterday we bought two Bliss yoghurts and upon arrival at home, one of them had expired 4 days earlier. We tried to take it back for an exchange or refund but we were told that neither could be done because the cashier who served us had knocked off, therefore we must come back again the following day. My wife and I tried to explain that we live quite far and we needed immediate intervention but we were ignored and told nothing could be done about that. As a result, that meant we lost our money and our child was crying because she was certain that she will have her yoghurt. I'm disgusted by their service and even when you're there to fill up, you'll find two attendants on the shift and you're going to wait ages. All I'm saying is, I need my money back. I have the receipt for my purchase.