Baseus Powerbank Replacement Failure

Around five months ago, I bought a power bank from Media Markt. It was made by the Baseus brand. However, it stopped working shortly after I got it. They want to subtract the cost from the length of the warranty. I agree to get the money back. I want either the exact same product or something similar. If you don't fix this, I'll have to complain to the Consumer Arbitration Board. I want my complaint to be taken care of and fixed.