No service in cash crusaders

Good day, I bought a guitar from mams mall Pretoria. As I write this I just got out of an argument with the supervisor(cannot disclose the name) of the store... It is now 2 weeks since I bought the guitar and still cannot tune it, I tried with different tuners and still no positive outcome and now they tell me that I should came before seven days, which is understood but with no one stating the 7 days on the till when we were buying and when we state the issue the supervisor response is vastly unreasonable.

I asked the supervisor to call someone who can help me, they say they can't so I now believe that cash crusader mams mall is good at taking our money with no assistance for their faults