Original Apple Watch – Apple watch blocked by ICloud

I recently bought a used apple watch series 1 on vinted, sold as working is in good condition received in good condition but blocked by i cloud,
I contact the seller so that he overcharges his icloud account (at the time of the problem on 25/12) but he assures me that it is not on his account despite the correspondence of the email addresses. despite several relaunch no news.

I would like to know if it is possible in store (apple certified) to unlock apple watches? and is it worth it or should you buy a new one?

Thank you for your help
good night

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