If you are receiving an error message saying "Sorry, an error occurred saving the topic: Could not activate monitor, company is inactive or non-existent", it could be for multiple reasons.
First, make sure all the rules in the Monitor are correct and a title for the monitor is included.
If everything looks good and you still get the same error, make sure the company is active. The agency admin can look at the usage of the company to make sure the company is active.
If the company has been suspended, you won't be able to create a new monitor. The best thing to do is to email your Account Manager to gain access.