Faulty phone

Bought a phone on 01 May 2020. Phone was slow, tried to update software, still slow. Returned on original packaging on 10 May 2020 for exchange, they said the can't exchange because it's past 7 days, it had to go in for repairs that could take up to 3 months. I complained, the sales lady said the ram of the phone is small so I should get a memory card. Bought the memory card and it's still super slow. I had the phone for 9 days and now my only option is a repair that could take 3 months. What should I use in the mean time?