Dishonest merchants. Ordered small but during pick...

Dishonest merchants. Ordered small but during pick up was charged a large. I told them I ordered a small and they said there are no small. Showed them their phone site and small was there at cheaper price, they apologised but said they already cooked the large and ask if I was ok. I took it but then was charged more than what I should pay again when I checked the receipt later.