This is probably not any consolation to you but as a suggestion. None of my charges come directly from Playrix, they do not have access to my credit card or bank information. Instead, everything comes through Google Play. The attached screenshot shows both the e-mail I get from Google Play and how it shows up on my bank statement. If there are two charges for the same amount, I contact my bank and dispute the charge and let them investigate the legitimacy of both charges. If it is a duplicate charge, the bank will credit my account and they have a way of getting the money back from Google.
So, from a certain point of view, Playrix is correct, all purchases come through the "app store" where you got the game and all charges to your account are posted by that same "app store". As your "billing agent", the phone provider should have a way for you to dispute the charges or at least investigate on your behalf.
Also, you should have some confirmation e-mails from Google Play and if that's the case, you can see if one or two charges were made. The confirmation e-mails should contain a "transaction code" which somebody should be able to track back to a bank or billing event.
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