So Fox News couldn’t deny the commercial, even if they wanted to? Sorry, I’m not familiar with how ad purchasing works.
It all depends on where the ad purchase came from, which we don’t know.
1. The purchase could have been made directly through News Corp (Fox News’ parent company). In which case they could have influence over its airing. Of course, then you get into a lot of legal issues if you deny it so you have a whole mess of lawyers involved.
1a. You then have another issue which is if the ad was purchased directly from this PAC or was it purchased through an agency thus, potentially masking who it was actually supporting. (yes, the network would still see it before it ran but by that time, the contract would be in place.)
2. The purchase could have been made through the cable or satellite provide for national airing. Example, they could have gone through Comcast or Direct TV and purchased the ad time for national broadcast over the time allotted for national purchases through them.
3. The purchase could have been made through the cable or satellite provide for the local commercial allotment. These are like how you would see your local car dealers or other businesses purchase.
Most likely it isn’t 3. It could be one or two.
This is why I’m not crazy about boycotts over indirect advertising. You don’t know who or how the purchase was made so you could be targeting the wrong group.
Better to promote what you believe and fund the PACs that run ads supporting your positions.