Mophie batter pack issues - no solution provided

Purchased Mophie battery pack from Istore waterfront. Within first 6 months the charging cable became 'loose' & provided intermittent charge. Returned to Istore & it was immediately replaced by a consultant, no qu's asked. A few months later, same thing happens. Requested to speak to the manager (who only contacted me 2 weeks after initial in store complaint) and explained how the batter pack is used & that I'm at a loss as to how/what has caused the damage a second time over. His feedback was that I must be causing the damage, can not assist due to the case being worn (the quality of coating is so poor that it scratches off with light touch of a finger nail), offered no guidance on how to use the product (it seems unlikely that the exact same random physical damage could be caused twice in a row without doing something incorrect or the product being faulty), offered no alternative solution, no suggestion or desire to figure out the route cause of the problem and finally when I offered to purchase another one and explained the exact manner in which it would be used, he again was not willing to accept any responsibility or desire to assist if the same thing occurred a 3rd time.