Pathetic service

I got a AIM 50" t.v at a pick n pay in middelburg which has 3years warrenty, but now when i return the t.v to the store they are telling me from the repair department that the serial number on the t.v is not one of their devices but its the product from the cash reciept and on the box. So how can Pick n Pay sell me an item that has warrenty on it but now they cant repair it thats completely unprofessional and pathetic service. I will never purchase anything from pick n pay ever again and will take my services to other retailers if i must including paying more.