Free trial expires but can keep having free trials

HI all.

I am currently using Paid Membership Pro in conjunction with Learn dash and offer a 5 day free trail. The issue I am having is after the account expires the person can re sign up again using the same email address and commence another free trail again and again?

I feel as a basic part of restrictions this should not be allowed after the expiration date. Can you please assist or advise how to stop this from happening. I do understand that the person can register under another email address but as a basic restriction they should not be able to re register using the same email address unless paying?
look forward to any feedback.

Regards
Zelldun