Contact the seller first for purchase problems
Ask the merchant to fix it first; a good-faith attempt with the seller is a condition of the claims-and-defenses right.
Call your card company
The CFPB says to call right away, then follow up in writing.
Send a written billing error notice
Write to the billing inquiries address with your name, account number and a description of the error, so it arrives within 60 days after the first statement showing the error was sent.
Pay the undisputed part
You can withhold the disputed amount and related charges, but keep paying the rest of your bill.
Escalate if needed
If the issuer doesn't follow the process, submit a complaint to the CFPB online or at (855) 411-CFPB (2372).