Hi @BriaenLaerson, thanks for your post here in the Community - welcome!
You can't cap the data usage from our side, but you can set a Spend Cap up on your Virgin Mobile account online, which means if you do go over your allowance on data, your spend cap will ensure you won't be charged more than what you've set. You can even set £0 as your spend cap which means you won't be charged at all once you've gone over! It will mean all allowances will stop working at this point though too.
As @enlli has mentioned though, you've touched on $ as opposed to £? Are you based in Ireland perhaps?
If you are, I'd recommend following the below avenues here to contact Virgin Media Ireland here.
Many thanks
Tom_W