@artopium yes I have spoken to the owner of @boomerang and it seems they have been having some technical issues lately. He has assured me that they are working on it and plan to refund anyone who had a missed bid including yourself.
As for being able to trust the voting bots my recommendation would be to use the ones with both the auto-refund icon and the purple check mark icon as those will be the most reliable.
I run the @postpromoter voting bot myself and personally guarantee that it will work correctly or your money back.