Here's a suggestion to raise your personal productivity level and greatly reduce the annoyance level for yourself as well as users:
Build in a mechanism that alerts the user when he has placed 49 calls in one day. Perhaps a big red warning sign before he makes the 50th call would suffice. That way, after making the 50th call, only those who knowingly make the 51st will be blocked. This will greatly reduce your frustration level as well as help the users know that they are unable to make more than 50 calls in 24 hours.
Otherwise, without warning, the user is shut down with no knowledge of what happened or why it happened. He is left wondering if the service is somehow substandard or is part of a trial that requires some further paid subscription. Simply terminating the use often forces the impatient user to set up another account, which does not accurately measure usage. Moreover, anyone who later is interested in buying the platform and user accounts or even simply selling advertising on the platform will recognize this is a severe limitation of head-counting users.
The proposed warning will serve to help you and all who use the service. Thank you for your consideration of the imperative need for this important FireRTC function that does not yet exist.