Agreed that flight time should be chargeable. However, it is also loggable so overall won't make any difference to your overall PPL hours, just maybe a dint in your weekly cash flow.
On the other hand, if your instructor was talking to you about improving your flying, then I would say that it's a briefing and you shouldn't be charged for it. Groundschool would be "chalk and talk" and typically involve theory etc on say, Met or Nav. I'm not aware of there being any minimum groundschool time for PPL; I had none!
Cheers
Whirls