[mothered]

do you have an idea of a pretext in case they ask me to send the pair back? It would be impossible since I have had them on my feet for 2 weeks.

They refused your return which Is absolutely no fault of your own, so you decided to wear them.

They're at fault for noncompliance.

And, when making a claim from Paypal with the above mentioned arguments, how does it work? I have never done this before.

In your PayPal account, go to the PayPal Resolution Centre and follow the onscreen prompts.