Hi Sorry for your problems
Have a look through the following support page https://support.brave.com/hc/en-us/articles/360055013431-Why-don-t-I-see-any-Brave-Ads-after-enabling-them- which goes on to look at some problems that can occur on specific operating systems. Also there is a new post that takes an in depth look at things that can go wrong. PSA: Friendly Reminder For People Having Issues with Rewards/Ads
Hope one of the above helps