You should google the term 'merchant of record'. In this case Stripe is the merchant of record. If you bring your own merchant account then you are the merchant of record. In the first case it is Stripe that gets paid, in the second case it is you that gets paid. Either way, in this case the transactions will be reversed so it looks like soon nobody will have been paid. Stripe reduces your liability by acting as the merchant of record but the fact that that liability shifts to them gives them certain rights - and obligations - with respect to the funds, and a unilateral refund is part of those rights.

The moral of the story: do not enter into an agreement without understanding the terms and the practical implications of those terms when applied to you and the relationship with your customer as well as the transactions themselves if you don't want to be surprised by some of the potential outcomes.

And Stripe isn't a Merchant of Record. They even have a specific product to overcome this, Stripe Tax.

According to all of the information the OP has given they are in this case. If you have evidence to the contrary I'm all open to it but it does not apply here unless you have information that contradicts the OP in a believable way.

Also: note that Stripe has all kinds of technical countermeasures in place to detect money laundering and other terms violations and it may well be that everything looks totally above board to an outsider whereas they have valid reasons to deny a party service.

The evidence in the services that Stripe provide, they do not handle taxes for you. They act as a payment gateway provider with some software add-ons.

Yes, so? That doens't mean that Stripe isn't the merchant of record. All that matters is whose name shows up on the credit card statement. If that's Stripe - as it usually is because it is their merchant account - then that's Stripe. Bring your own merchant account and it will be your name that shows up. Stripe can be IPSP and PGP depending on the circumstances and the story the OP told here strongly indicates that they are using Stripe as an IPSP.

The difference between a payment service provider and a payment gateway is substantial, in the first case you likely won't ever see the customers card details other than what is required for shipping, in the second you will have all of the data including CVV and expiry and you will have to deal with the associated overhead.