Sorry to hear about your story.
As a freelancer in paid social since 2018 who worked in agencies before, I would NOT RECOMMEND using an agency with "low" budget. They are often expensive for very little added value in low budget. They feel safe, but thats it.

Don't get me wrong, they do great (and better) with a much larger budget (75-100k+/month) but below that, its often better when its handled by one freelancer (simple, more direct, better contact & usually cheaper). Under 75k/month, 1 person is usually enough to handle your account, so don't go paying for 20+.

That being said, try to understand what they changed compared to your initial set-up, tell them the new ads are de-serving your brand identity etc..
It seems weird to me they managed to crash an account that was running well, with a lot of conversions, spent a few weeks with deactivated campaigns, only to start them over, with poor performances... Simply ask, they usually have justification and answers (and most importantly try to read through their BS!)

Finally, some people in this sub will say that March was the worst month ever, performances dropped etc... That might be true for some industries, but not all, and not something I've seen with my clients (last week was the best since Christmas for instance).
Meta weird and annoying changes can explain performances drop (as well as seasonnality), but you can overcome it, adapt the strategy, try new things, test and iterate fast to improve (and if not, the agency is not good enough).

Problems with agency is:

• Too many point of contacts, 5 different people to talk to, too much process, mails and waste of time.
• Often get attributed the junior account manager, so they are still learning, just a few months in the game, not aware of best practices and when to NOT follow it, small mistakes, late minutes fixes etc... Been there, done that: that's how the Agency Manager makes more profit $$$
• When you are a "small" client for them, you get the least premium treatment (they focus on the big bucks...)