
They say the bets were refunded because the displayed league was different:

This is what Wikipedia says:
U-19 Thailand Championship, commonly known as Coke Cup Thailand by title sponsor Coca-Cola , is an annual nationwide youth under-19 association football tournament
Other books and live scoring sites also said U19 League:



An article on a Thai news site says the following (google-translated):
By competition will be divided into 8 groups covering the whole country, consisting of
Group 1 (Bangkok), there are 12 teams competing between 22-27 August 2019 at the Greg Koo Sai Mai United
Group 2 (Southern). There are 14 teams competing between 18-26 September 2019, Satun Province,
Group 3 (West), there are 10 teams competing between 1-6 October 2019, Kanchanaburi Province,
Group 4 (East), there are 12 teams competing between 15-20 October 256 e. . Chanthaburi
Group 5 (Lower East) with 10 teams competing, 25-30 October 2562 e. Si
Group 6 (Northern Region), with 10 teams competing between 12-17 November 2560 e. Phetchabun
Group 7 (Upper East), there are 10 teams competing between 28 Nov - 3 Dec 2019, Loei Province.
Group 8 (Upper Northern), there are 10 teams competing between 9-14 December 2019, Phrae Province
https://www.innnews.co.th/sports/news_449311/
So there are 8 groups each consisting of 10-14 teams. The group phase is played in a single round-robin format. After that there will be play-offs.
It's actually similar to US sports NFL, MLB, NHL etc or UEFA European Championship. There is a first phase (groups, divisions) and a second phase (playoffs, knockout phase). Nevertheless it's called
- National Football LEAGUE
- Major LEAGUE Baseball
- National Hockey LEAGUE
- European CHAMPIONSHIP
So if Wiki says it's a national U19 championship who cares if it's officially called Coke Cup for sponsoring reason? Probably they called it Coke Cup because of the alliteration (Coke Cup). It sounds better and more pithy than Coke Championship, right? I think that's the only reason.
I had a longer conversation with the live chat agent and he said the traders will double-check. After a while he said "the decision is final" and left the chat. That was it.
I think this is a ridiculous reason to void bets post-match. My guess is the real reason why they voided the bets was that there was a live drop from +0.25 to -2.5 and Prachuap won 7-1. They just looked for a pretext to avoid paying.