My instructor charges "Ground instruction" without teaching me anything

Hi guys! I just want to check if this is normal or not. So I've started to taking flying lessons and I think the instructor is overcharging me. For example if I go there at 8:30 and leave at 11:30 and log exactly 2 hours, he charges me an hour for "ground instruction" while in fact he's not teaching me anything. During this extra time I'm doing weight and balance, pre-flight check up, ... , ALL BY MYSELF. He's not even there! Just want to know how was your school and what should I do with him. Thanks