You could remove those contacts and not be charged for them however if you only email someone once that started a trial account you’re doing your business a disservice in our experience.
As someone who formerly lived in email marketing, the onboarding flow for a trial signup was usually a 7-day flow, 2 emails on the first day, the first was very transactional and automatic for activating your account, the second one was still automated, but a few hours later, and from me (the developer of the product) providing my personal email for any questions. Then one email per day with a tip on how to use the product effectively with mini-case studies from customers.
This converted at 9-15% depending on time of year and product. We built a lot of micro-SaaS offerings.
Our conversion before we did this onboarding multi-touch email approach was closer to 1-2%. These onboarding emails really do work with get a customer engaged and using the trial instead of signing up, and forgetting about it because it was free.
After that, if they converted, they would be moved into a different flow with a less frequent emails (weekly or monthly depending on the product). If they didn't convert, we had a second flow that would lead to an extended trial or discount which would convert another 3-5%.
Effective trial marketing is very important to sign ups. Our "marked as spam" and unsubs never went above 2% because we were providing value in our emails for a customer who signed up for a trial for a reason.
Yes, we send follow up emails to remind them to get things setup. But I don't send much mail beyond that. I do not like sending spam. Conversion is around 10%.
this is just extortion in pricing. no competitor does this. good luck.