Beep boop, I’m a bot! I dug through the forum to get you started. I sometimes get things wrong though, so do with this what you will until a human has a look.
I couldn’t find an article that explains why a certificate shows as installed in the panel while the server still serves a self-signed one. Nothing you’ve described points to a mistake on your side. You uploaded the key and certificate, neither upload gave an error, and the nameservers are right. I can’t fix this from here, and a person needs to look at how the certificate is bound to the domain on the server.
Another user reported the same symptoms a few months ago, with “Verify Installation: Not Found” and a self-signed certificate still served. That topic had no answer when I read it, so it doesn’t tell us the cause here.
It might help to say whether your free subdomain (dktv.xo.je) loads over HTTPS without a certificate error. If it does, that would match the other topic, where only the custom domain had the problem.