About 3 years ago I was refused a 30 stamp at mae sai border because I had already received an extention at Chiangmai immigration.Would this still be their rule or would they give two per year regardless if you got an extention?

They no longer stop people because they had gotten a 30 day extension.

They stopped allowing a crossing for visa exempt entries until after the 2 entries per calendar year rule went into effect in January of 2017.

I did 2 Mae Sai trips this year + extensions at CM immigration afterwards, one flying trip to KL in between of the 2.
Didn't have any problems or questions doing so (Dutch national). Fun trip as well!