What I understand on the case of under 18.5 was the bet is already lose regardless if the game still continues or not while in your case, there’s a chance that you can still lose your bet if the player didn’t retired earlier since the retired player has a chance to score more and close the gap to erase your margin.
If I'm not wrong this is the rule being applied to the OP's issue.
This can be found on their general terms and condition under their general betting rules.
Here's the link for that General Terms and Conditions
For OP, I agree to what Gianluca95 has said, better to bring it up to their thread not create another thread on this section.