BAD SERVICE

I bought a phone at Markham Jabulani Mall first week of May 2020,hisense infinity E30 but now my phone went blank is not working anymore and when i return to the store i was told that they want a slip i explained to them that i lost my slip due to the funeral so i cant find the slip so they wont fix my phone because i dont a slip anymore but i do have box of the phone and the charger