When you see your bet marked as "Void", it essentially means that your bet amount is returned to your balance. If you have a multi bet where one of them is voided, then it simply means that odds for that one is counted as 1x. Odds on the bet slip won't be updated, but the payout will be shown correctly. Reasons for why a bet is voided could be quite varied, and that's better explained in our Sports Rules Page.
Here we'll hopefully offer a way to see this from a different point of view. If you check your bet and notice it would have been a loss, then you got lucky in a way and avoided that, so you can consider it a good thing.
If however your bet could have been a winning one, you might feel cheated, and we understand that as well, but please check the reason for it and try to understand it from the sportsbook's from our point of view as well, as there are always 2 sides to a story.
Of course, if you need a case to case explanation, you can always contact us on live support chat.