1. Make sure none of what they say is true.
Not even a little bit true.
2. I rather doubt that a loss of "ratings" amounts to a compensable loss.
You'd have to show that you lost actual dollar-earning business, or
that in some other way it damaged your reputation, which in turn lead to dollar loss.
Your mere belief is not enough.
What might happen is not enough.
3. Defamation actions costs thousands to even start,
more thousands to run, and can take years to resolve.
Be sure that the amount of money you have lost
is vastly greater than the costs of running the action.
Also, be sure that you can afford to lose. Because if you do lose,
then you will be paying not just your own lawyer,
but theirs as well.
4. No, you won't get Legal Aid for this.
No, you won't find somebody who will do this on a "no win no fee" basis.
In fact, if it was me you were engaging, I'd be looking for what lawyers call "security for costs".
That is, some reliable sign that can actually pay even my bill.
5. If all you have "the principle of the thing", then you have nothing.