Online store charged my card twice for one order

A duplicate charge for a single transaction is a billing error the trader is obliged to correct promptly once you notify them, and unreasonable delay in resolving it can itself be treated as an unfair commercial practice under the Consumer Affairs Act, Chapter 378 of the Laws of Malta. Send a written complaint (email is sufficient) referencing both transaction reference numbers, your bank statement showing the duplicate charge, and a clear deadline, such as fourteen days, for the refund to be processed. If the trader still fails to act, you can dispute the duplicate charge directly with your card issuer or bank, which can often reverse an unauthorised duplicate transaction relatively quickly. You may also file a complaint with the Malta Competition and Consumer Affairs Authority (MCCAA) about the trader's handling of billing errors, and if the amount remains unresolved, the Consumer Claims Tribunal can order repayment.