That happens quite frequently to our SaaS where people need free access to a new API key. We try to block multiple registrations but there are people who also invest into proxies to circumvent this protection...
people who want to bypass those restrictions can easily do it. It is trivial to get a bunch of mail addresses to use, even without "disposable mail" providers. People who try to abuse the trial period over and over will do. Blocking the disposable mail providers however also blocks users who are curious, but not yet committed.
I argue that maths is negative for your business and a better approachbis to make it easy tonget started, but show them clear benefit of switching plans. Maybe a cheap entry level plan with a small set of convenience features, not available to the test account.