phone battery not charging

I bought a mini mint phone from pep on 04/10/2015 and the battery is giving more problems than joy and I phoned pep to complain and I spoke to russel and he suggested that I get a new battery so I can test if the problem will go,but I am in no position to buy a new battery for a new phone which is less than a month<br> old.please I need to get clarity as to what need to be done