Please never use services that sell subscribers. It’s the worst thing that can happen to your channel. You will damage your YouTube channel forever. YouTube’s fake engagement policy is very clear about it:
YouTube doesn’t allow anything that artificially increases the number of views, likes, comments, or other metric either through the use of automatic systems or by serving up videos to unsuspecting viewers....
If someone is offering you the exact number of new subscribers, there will be bots or people who are getting pennies for subscribing to your channel. But none of them will watch your new videos. Because bots don’t watch videos, and if there are real people, they usually don’t use their work channel to watch the videos of people they are fooling.
The only legit way to increase engagement is Google Ads. And this is what Prodvigate does.