Stand your ground and don't be easily intimidated by the boys (and girls) in brown. They have no legal grounds to deny you entry if you meet the 3 requirements (cash, hotel, tickets). You never overstayed, you are not blacklisted. Everything they say about "staying in Thailand too much" is pure intimidation.
I've been in Thailand 3+ years as a "tourist" and they tried to intimidate and give me sh*t countless times. I know all their tricks.