Yes banks regularly seize money from accounts for hundreds of days and refuse to discuss it with paying customers /s

Actually, they do. And they will hold reserves on accounts for many months to over a year if they suspect it may be fraud. The acquiring bank does this because the risk of a chargeback is high and their ability to recoup the funds may be diminished with a small account.

I've been in high risk merchant processing for almost a decade. The merchant may never get the money back until they close the account completely and wait half a year for a check in the mail.

Sure, and OP understands that. But, there’s apparently no effective resolution process, especially one involving a human.

What would you suggest the OP do to resolve their issue?

There is no "resolution" to the situation. His account has a reserve on it and it may stay there for the entire lifetime of the account. He has to just deal with it.

Reserve isn’t much of a problem. Never getting your funds is different.

A reserve is to make sure that the funds are there to cover the check in the event it may bounce. Checks do not take 120+ days to complete.

Credit card chargebacks can be initiated a half a year or more after a transaction has occured so yes, the reserve is in place to reduce the risk of losing money of the merchant bank from this event.