Offering restitution after a customer went to the media is not enough. If this is a systemic problem (and indications are: it is), you have to take steps to avoid these scenarios in the future.

Having a customer service that actually responds to issues meaningfully would be a first step, but that's only the beginning.

There's a technological solution to this. If you know that for whatever reason some transactions might never complete on your end, one of several obvious solutions would be to introduce a timeout after which the transaction is rolled back automatically. That means introducing a batch process to at least trigger a manual review of these cases, and possibly even an automated cancellation with repayment. Doing that within a business day of receiving the money wouldn't be out of order, maybe even make it an hour or so (this is supposed to be a fast medium, right?)