So the CNAME is pointing to your e-commerce platform, which is not
www.yourdomain.com if I understand correctly.
I presume you did this on your domain name and not on the hostname record.
Normally this shouldn't matter and you still should be able to login via
https://yourdomain.com:2222 unless there is a redirect present somewhere.
As alternative you can login using any other domain on the server for example
https://otherdomain.com:2222 using your own credentials.
Or like earlier was done, try via the hostname like:
https://server.domain.com:2222 which should also work.
If these don't work then something else is wrong. However, in that case I wonder exactly where that A record was removed.