This is probably more a question for your hosting provider. Let’s Encrypt only issues certificates, Let’s Encrypt can’t install them into your site. It’s up to you or your hosting provider to do something with the issued certificate.
The only advice I can give is “use the previously issued Let’s Encrypt certificate”, but how is a whole other question, especially because you answered “Yes” to the question about the name and version of the control panel you’re using… And “Yes” neither is a name nor a version.
I only have a little to add to what @Osiris has already mentioned.
It appears that https://tourisme-maredsous.be is currently serving the default certificate from OVH and not your previous Let’s Encrypt certificate. If you simply reinstall your previous Let’s Encrypt certificate as @Osiris has already suggested, you should be good for the time being.
Thank you Osiris, the control panel concerning the certificate indicates that the new certificate ordered is being installed (ssl EV procedure). I therefore do not have the possibility to reinstall the original one.
I have already sent a support request to the hosting company but I don’t have an answer to my question.