Lesser conversions - users signup with new email every time trial period ends. How to deal with it?

What is the % of users signing up for your product free trials (without card) with new email addresses every time their free trial period ends? I hope trials even with credit cards would be having similar use cases. After all, we offer cancellation anytime within the trial period. We need unique email addresses, but somehow restricting the same cards may turn out to be favorable or unfavorable. How are you dealing with it?