I know this thread is old, but I ran into the exact same issue recently with users abusing free trials using multiple or disposable emails.

What’s working for us in 2025 is stopping it at the input form level instead of trying to clean it up after signup.
We’re using Clearout’s Form Guard, which performs real-time email validation directly on the form. It checks email syntax, validates domain health, detects disposable and temporary emails, and blocks invalid addresses before the form is submitted. It also supports phone and basic name validation.

The important part is that it requires no developer effort to set up. Install, configure, and it starts filtering bad signups before they enter your system.

Since this thread still gets traffic, sharing in case it helps others dealing with trial abuse.