“Promo credits” charge - any ideas?

[mcshane]

We returned from an amazing trip on Venture in Antarctica last week. I noticed that my credit card was charged slightly more than I expected, and when I checked, it mentions “Promo credits” as a $24 charge. I will obviously call on Monday when they reopen to check what this is, but has anybody any experience of this? We did not buy or sign up to anything like this! Thanks. 

[rallydave]

Agree, how can a credit become a debit you are charged for???  Interested in their explanation.