Not what you want to hear, but any system failure is down to you. You are responsible for the security of any tech you use and staying safe online.
If your PayPal account has been used, you need to contact PayPal. You say that you've been in touch with them and reported the payment as unauthorised, but are not getting anywhere. Why not? What reason have PayPal given?
How did somebody manage to access your eBay and PayPal accounts? Were you opted in for faster payments so that all they had to do was to click the 'buy' button without putting a password into PayPal? Opt out of faster payments for eBay purchases and any other sites you use it for, it's much better to have to input a password to authorise a payment. If your eBay account is compromised, it can't then be used to make payments.
You need to work out how your account was compromised in the first place. Presumably you have up to date security on all of the devices you use? You should be aware of how to stay online, and each site that you use (particularly financial ones) MUST have a password that is unique to that site. Your most important account is actually your email, because once somebody has access to that, it's a gateway to every other account you own.
Most accounts are compromised becuase you've logged in on a network that's not secure (perhaps when out and about), left yourself logged in somewhere, or via a phishing email. An innocuous looking email pretending to be from PayPal or eBay arrives, it features a link which, when clicked on, leads to a spoof log in, where your password is captured. The golden rule is never to click on any link in an email, but to straight to the site in question to see if there really is an issue there.
