Definitely contact the museum. Even if they confirm everything via phone. Get several legitimate emails of management and any secretaries and cc them all in the email. (Management is likely who would have to issue the refund and their secretaries would get the email to them)
First off call and email them again (most importantly email for paper trail). Attach everyone to the email that have the authority to issue refunds. Next go to your bank and show them the proof of them sending back a refund. They should be able to help expedite.
I would definitely reach out again and make it known that you still haven't received a refund as of yet plus maybe reach out to your bank as well so that maybe when it's being processed through them they can notify you
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