Chances are that (at least) one of your customers denounced you @Coinpayments for some type of misbehaviour or broken promises.

Furthermore, unless the jurisdiction you are residing in, isn't a third world country,
chances are that you are technically breaking the law by accepting other people's money for engaging in trading activities.
(unless you are officially a "professional money advisor/consultant" or "professional investing/trading business relying on investors capital",
registered with the district court/chamber of commerce or other authorities/agencies depending on your jurisdiction)

Most civilized countries simply require such a registration, to halt and discourage frauds and scams perpetrated by thiefs and con-artists,
as they are usually reluctant to reveal their name and true identity by registering (if they have intention to steal from their customers),
and thereby offer some protection to their population.
Some countries like the U.S. may even require your customers to have an "accredited investor" status, depending on the securities or the
level of risk involved in trading those securities on their behalf.

However, if you have not committed any wrongdoing and always acted in "good faith" and in the best interest of your customers, i agree
that Coinpayments shouldn't have frozen any funds, but rather asked for an interview or conversation, in order to evaluate the situation.
If they refuse to work with you in future, i agree that they should have given you a warning or a time-frame until when they will close your
account with them, but at least process the last transaction/s. (as long as there are no strong reasons not to)