SSL Certificate keeps changing on IIS7

The problem is the SSL certificate just keeps on changing. If we restart our modem the certificate would show just fine for a couple of minutes then it would start giving out a wrong SSL certificate like this:

http://i.stack.imgur.com/HY9JD.png

If this happens I just unbind the SSL protocal, rebind it again, restart IIS7 and restart our modem and it would work fine again. The SSL certificate shows fine when the server is accessed within the local network at all times, but if it is accessed remotely it gives out the wrong SSL certificate.

I already removed and reinstalled the SSL certificate along with Intermediate certs and this still keeps happening.

Also one thing I tested, if I disconnect our server from the internet and tried to access the server from a remote computer (with clean cache) it would still show the invalid SSL certificate when accessed using https but when its http only it would show that the server is unreachable. Shouldn't it say that the server is unreachable as well when accessed through https?

We tried setting up different SSL certificate from different SSL providers as well and the problem still persists.

I'm stumped on what keeps doing this, maybe anyone here experienced this already or knows how to solve it?