I was told at a local 7-Eleven that payment by credit card is only possible for amounts of 200 baht and up. Like in good old pre-covid days. Is that what they call cashless society?
It doesn't mean they did that lawfully. Anyway, I don't know what exactly you told them, how you answered their questions. I've been questioned many times, and always allowed in.
I've been in Thailand as a tourist since the beginning of 2020, never leaving for more than a few days. As long as I don't stay longer than each stamp allows, it's not a problem.