That’s just very rude.
Can you elaborate on what type of complains you get?
Most of the time I have seen teachers talk to parents when they come to pick up after school - that is to reinforce good behavior at home with parents supervision, so the child can improve his behavior.
If your child is good at home and the teacher complains, then REQUEST that you can be allowed to WATCH the child in class the next day. Which means, you will be observing the child’s behavior but without the child knowing you are there. Like sit at the spot where you won’t be noticed by the child.
It’s really not good for the child if he keeps hearing teacher say things to his face. Act NOW!