Refusal to return expired items. Accusing customer of lying

We bought a few bottles of coca cola from the store in Ottery and decided to return it due to the expiry date being past due. The merchandise manager Riyaad says that 'his' products are not expired and we brought these good from another store and that we are lying, even though we have proof of purchase. Who gives this guy the right to accuse us? We even had proof of purchase(3 slips). Refusing to take back ********** quality goods is one thing, but accussing somebody of lying is another thing. Utterly disgusted by this guys attitude. People like him will never get far in life and will only destroy your brand Pick n Pay and customer service. Sickening attitude.