Exchange and Refund policy

Bought shoes on the 10th January 2020, wore them on the 12th ; noticed that they were faulty, went to the store for an exchange, didn't have size, Beatrice Mpeta tried to get size from other stores with no luck. Decided to return since I didn't get the size now they refuse to refund saying they will give me a gift card which will buy in their chain store, I refused because I saw the same shoe somewhere else and that I bought with cash not by gift card. At the back of their receipt clearly state that they will either refund or exchange merchandise if it has default for 6 month period. So why am I not refunded? Is it by force that I must buy from Jet? Please help me with this query.