I am involved in a scam scenario with CJS Sales & Services LTD

[bald_spectator]

So I tried to buy a STEAM-KEY from CJS Sales & Services LTD (cjs-cdkeys)
Paypal logo was present on their site(as one of the available payment methods) - I didn't hesitate to use it
Purchase required a personal data entry(that I now regret entering) and once I was done with it - I went through a PayPal linked payment with a confirmation code.
As a result, I saw this as a success message on Paypal

And this on a web-site

So here you go - they say that I payed with an incorrect checkout data, even though those 'Guest Checkout' and 'GUEST CHECKOUT' values they shared with PayPal were set themselves(I provided complete personal data for them before the actual checkout).
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Now my question to all who is willing to help me(not the scam website): Should I contact their support like they wrote in the notification message?
Or should I leave this and wait till the transaction fails? It is currently in 'Pending' status

I read(on a couple of review sites) that they don't respond to their customers for weeks, and in certain cases 'never'.
If I should write them, what information should I share with them? (so that it won't cause me any further money loss)

[PayPal_JonK]

Hello @bald_spectator,

Welcome to the PayPal Community! I'm sorry to hear you're running into a potentially fraudulent merchant. Once that transaction completes, you may have the option to open a dispute. However, we do normally recommend trying to request a cancellation / refund first through the merchant. If they're unresponsive and you do not receive your item / service, then we recommend Opening a dispute through our Resolution Center. 

I hope that helps a bit, 

 - Jon K