Even though its out-rightly wrong for a service provider to just deny one access without adequate notification morally, but they are covered by their Terms and Conditions which you have accepted before allowed entrance on their platform that they don't owe you any notification to get to the point of deactivating your account should in case you have violated any of their Terms. The best is to move on.
Yes, it's my fault too since I'm also one of the thousands of people who have reading disability concerning the terms and policy when registering in any website.
They should suspend my account in the very first place when I used their service to send emails with cryptocurrency content for their
free plan not after I top up my account for sending emails to more than 2k subscribers and to get higher limitations of sending emails monthly. But anyways I already moved on.