AUSTRALIAN METV ~ HELP!

- I was issued a 6 mth. multi entry tourist visa from australia on 1 sep 2017.

- Entered thailand on 13 sep 2017 (chiang mai).

- After 60 days i extended for another 30 days at immigration (90 days total).

- Did a successful border run to tachileik, myanmar.

- Got another 60 days upon reentry, extended that again by 30 days.

Now im a week off from a total of 6 months total stay in thailand.

Did a border run to tachileik today expecting another 60 days entry.

Now the border control officer has told me my visa is now expired and hes only given me a standard 30 day no visa entry.

Their reasoning for saying my visa is expired is that my visa says 'enter before 28 feb 2018' (highlighted in red below).

I was under the understanding that it meant my first entry from australia to thailand had to be made before 28 feb.. and was also under the impression that if i extended each 60 day entry by 30 days, i could get a total amount of 9months stay in the country from this single visa.

Can i go to my local immigration to have this fixed and explain whats happened? Or am i in the wrong (lol)...

PLEASE HELP