If I do a nmap scan from the internet i can see that the FTP port is open, but I have not enabled FTP service from internet. I used to have it open before, but I disabled it, the service is not running, but compared to other services I see that the connection is accepted but no login is possible.

Would it be possible to completly turn off the FTP service?

I have powered off the Deco device and turned it on, but this didn't help, so I have factory reset my deco devices. but there is still the ftp port open even after a factory reset.

All other ports are not answering to a request, and it would be great if all ports would not accept any connection so the device would not show as it self available towards the internet.