Terrible customer service

I purchased a cell phone at Woolworths in Cavendish 4th February. I explained to the consultant Cassidy Roman what I was looking for and my price range. He recommended a Mobicel device and talked me through the phone specs as well and the warranty process. He told me that if any software or hardware issues should arise within the first 7 days I can return the device, he also mentioned that that was the last model they had available. After setting up the phone, I downloaded my applications and started experiencing a lag on the device. I also inserted my 256g memory which slowed the phone down and also did not read the memory card. I returned to the store the next day to explain the issues and was told neither of the issues fell under software or hardware and they cannot do a refund. Memory card not reading and phone slowing down after downloading applications surely fall under software and hardware. The store is now refusing a refund and I have the phone for less than 24 hours