Gonna make extension soon but my 1 year lease is showing old passport number - got new passport few months ago - so what will Jomtien Immigration say ?

Who knows what they will say.

Take both passports in and explain it.

Passports get replaced all the time. If there's one place where they should know it should be immigration. Take the old passport with you and it will be ok just in case. They probably may not even notice or care. Your driving license maybe has the wrong number now too, nobody cares about that either. ( I am sure someone will come along and tell me otherwise, but you know what I mean).