Refused to refund me.

I bought a pulse oximeter in Novemberdue to probls in keeping safe the slipi tooka photo of the slip kept it in my phone. Now in January my oximeter was broken, they told me they are not considering the slip on the phone, they won't refund me, i have to take something else, i am not haggy with their service, they alwayshumiliate me, it's not the first time, ihave experienced this, kindly assist. N. Nzama