Undisclosed Call Out Fees

I reported a faulty passive - which is within the 12 month warranty period. When the technician showed up I was told the battery was flat and I can buy one myself an replace it. I was charged a R500 call out fee as there is only a 3 month warranty for batteries and this was 10 months after installation. This is clever as a battery will last longer than three months, therefore always outside of warranty. I was never told about a call out fee but was told this is in the small print somewhere, they could have told me to check the battery first and I would have replaced it, no call out fee needed. Now a battery will cots me R500 plus the cost of a small battery.