Poor Service

I bought a secondhand laptop at cash crusaders( campus square) and when they did the checks the battery had 80% capacity in a space of 3 months that laptop had to be charged for it to work and that 6 months warranty apparently doesn’t cover for that( I was only told this when I went there because of the battery issue) and they took the laptop for a “quote” for the new battery…I have been going to the store for updates and all I get is that the technician is still busy with it, when I call to ask when can I get this device back, nobody has the information and the person who assisted is always off and I am told to call again the following day.