Yes Multiple Entry - Not limited to 5 nor is this O-A Visa described as a 5 Entry in the online listing of visas at the Thai Embassy / Consulate website
Anouk van Neck... After settling the unintentional overstay (making it clear to the immigration officer that you misunderstood the visa dates). It likely won't change his/her mind much - but who knows? Next after getting a 30 Extension... you may plan for a 60 day Covid Extension... it should still be available.
But your explanation - use of terminology is totally incorrect. Your description of what you paid for is bonzo... There is no such thing as a 5 Entry O-A... it is unlimited entry and exit - if border conditions allow. Thailand land borders and regional land borders are closed.
The money requirement you speak of is NORMAL - usually expressed in Thai Baht Equivalent of equal to 65,000 baht equivalent a month salary in bank deposits. Or a one time 800,000 Baht equivalent Cash in the Bank. Which is equivalent in USD to $25,000 to, $26,0000 or even $27,000 in alignment with the prevailing THB / USD Exchange Rate - not $17,000 USD.
Bottom line you got an O-A Visa (last November? 2020?) and you don't know what you paid for - one example - there is no such thing as a 5 Entry O-A Visa... Did you use a Visa Agent? Or direct with the Thai Embassy / Consulate? I could go on but a waste of time
Not Correct... When in Thailand you go Immigration and file for a one year Extension of Stay... 800,000 Baht in your Thai Bank Account in your name only, file form TM.7, copies of passport pages, bank letter, bankbook, proof of residency (lease agreement. Go to the Immigration office get a list of all items required.