Shelve bracket of inferior quality

I bought three shelve brackets from chamberlains but unfortunately I needed four to complete the job, it was already past 15:00 on a Saturday, Chamberlains had already closed. I went to get a single bracket from builders warehouse (16th , March 2024)I picked what I thought was a similar item, it was R26 more expensive. Got home and installed the bracket, it fared really badly, it was flimsy and of inferior quality. Uninstalleed it and took it to builders warehouse atterbury faerie glen (17th March 2024), the manager at returns devision was cold and unsympathetic. I was told that I made modifications by drilling bigger holes on it, so they won't accept. I tried explaining to them that I had already installed 3x other similar looking bracket from chamberlains and there was nothing wrong with then, but thier product did not hold up. I'm absolutely gutted to have paid more money for an item which tends out to be of inferior quality. The bracket shouldn't be sold to anyone as it is flimsy and quite frankly not fit for purpose. I understand returning items in their original state, but when quality (strength) of an item is in question, May the store should seriously consider reviewing that particular item.