Pep store home

I bought a wall clock from pep home in carnival mall on monday 29 th november. I was in proses to move to own flat so on Wednesday the 30th i put the clock on wall it worked an hal an hour an then stopped. I bought new batteries thinking it was a new battery. I trew the box away and rhe slip cause it was working. I went back asking for a replace ment clock they refused as i dont have a slip i explained what happend and even showed my banking app that i bought it from them. I need someone to please asssit me on this.