How to retrieve funds transferred from PCS to a PayPal account

Hello,

I hope someone here can provide me with quick information as I am in a rather delicate situation.
I have put some items for sale on Ebay and leboncoin.fr
A person contacted me for a lot of books, offered to pay via Paypal, without specifying that they did not reside in Europe but in Switzerland.
I received the notification of funds transferred for the book lot as well as the shipping fees. I therefore proceeded with the shipment, and sent the information (service provider, tracking number) to Paypal confirming that the shipment was made.
Logically, the funds should be released but I am being asked for a tax of 600 euros, or 4 PCS coupons of 150 euros because my account is not recognized internationally and that the buyer resides in Switzerland and that my account needs to be authenticated as it is impossible to transfer Swiss francs to a Euro account.
Being unemployed, and living alone with my 4 children, we find an amicable solution with the buyer who advances 300 euros.
Being somewhat responsible for this very unpleasant surprise, I find her gesture reasonable and I purchase the two coupons myself, and sent them the two recharge numbers.
Within 10 minutes, I was supposed to receive my funds, however, another nice surprise, I received another message from Paypal saying, since the buyer’s account is outside Europe, there is another tax of 1200 euros, or 8 coupons.
First, I don’t know how they calculate the exorbitant amount of these taxes, and secondly, I don't even know if it's legal.
I am completely unable to pay this sum, so I ask to cancel the transaction and retrieve my 300 euros as well as the shipping fees, for the package that was returned to me.
I am told that it is impossible, and that I need to transfer the money to recover my funds, which is the selling price and shipping fees paid in advance by the buyer, plus the 1800 euros in taxes and 20 euros in shipping fees to return the package.
I admit that I am starting to think that this is probably a big scam because why would the buyer have advanced 300 euros in PCS and would still offer to advance 200 euros for the new tax? Initially, I thought Paypal was giving me a little gift and asking only for 300 euros, and in fact, I learn that she paid 300 euros which seems really suspicious to me. And as a result, after a firm reminder and threat to file a complaint at the police station and take the matter to court with my lawyer, the Paypal representative offers me to only take one coupon for 150 euros, and guarantees me that I will be reimbursed for my 450 euros paid, plus the transaction (selling price + shipping fees), plus 20 euros to return the package, and I will even have 500 euros in my Paypal account that the buyer supposedly transferred. This still seems too good to be true. So here it is, I just want to recover my two coupons as it has indeed been debited from my bank account since I had to pay for them in cash, and the 20 euros shipping fees for the first shipment and finally put an end to this very suspicious transaction.
Can anyone tell me if these taxes are legal or not, and what means I can resort to in order to recover my due and close the case quickly?