I don't quite follow how these scammers were able to attempt making you pay them $979.87 and $711.00 when they paid you $3.00? Were those separate transactions listed in your PayPal account after their initial $3.00 payment, just using the same PayPal email each time?
We would definitely recommend disputing those $979.87 and $711.00 transactions with PayPal (not just the $3.00 ones) if you haven't already. As for why those may have used the same PayPal email as an initial $3.00 purchase from you, perhaps the initial purchase was just an attempt to discover your own PayPal Email where you receive the payment, so then they could try to exploit some aspect of PayPal's system to "bill" your PayPal account for the other fraudulent amounts?
The fact your Transaction Log shows no download attempts were made for those purchases (nor for those more recent mail.ru
purchases you mentioned) may corroborate those orders were placed for ulterior reasons. Perhaps those buyers have not attempted to defraud you because PayPal has already fixed whatever exploit the earlier attempts took advantage of.
If you only became aware of those fraudulent payments via some email alert you received from PayPal, and you didn't see those amounts at all in your actual PayPal account, it's possible those emails didn't come from PayPal at all but, rather, were "phishing" emails meant to trick you into clicking a link in the email to bring up a knock-off duplicate of PayPal's site where you'd enter your PayPal login details for the crooks to capture.
Going forward, taking the free upgrade to a PayPal Business account will hide your PayPal Email from buyers and let you specify a business name to show them instead, as well as lifting your monthly receiving limit and letting PayPal's checkout site offer a card-based payment option for buyers without a PayPal account, among other business-minded amenities. You can take that free upgrade at https://www.paypal.com/UPGRADE
To go along with that, we'd also recommend changing your PayPal Email and Password, since the ones you've been using up to now may already be compromised. Once you do that, be sure to update the PayPal Email in your E-junkie Dashboard to match. That would be under Manage Seller Account > Edit Profile, where we'd also recommend making sure the Display Email we show your buyers does not match your new PayPal Email.