You can do a chargeback, but Booking.com bans you after - even if it is completely their fault

Isn't retaliation for chargebacks a violation of most merchant contracts with the credit card companies?

The one time I have had to request a chargeback I was basically told to contact the financial institution[1] in case the merchant tried anything funny.

[1] In this case Nets A/S who acted as a middle man between my bank and VISA. But I assume my bank would have said the same thing if they had the agreement directly with the CC company.

Suppose it is true, I would like to know what you would do after your account is banned. You are not a part of that contract so you cannot sue the merchant. And credit card company likely won't bother with a lawsuit because there is one person affected by this.