Sears Central air and heat unit

Sears installed a heating/cooling unit a few yrs back in my home. Ever since it was installed it never worked properly. So for the last 2-3 yrs Sears have charged me a maintence fee. So they can come out each season and either add feon or withdrawal so we can use the heat. It has leak and appears to be installed wrong. Im a retired man with little income.I dont know were else to do about this problem. Please help me