I can't see my groups on the website

I'm being able to send messages from my cellphone to a group, and I also receive messages from that group, but when I log to the web with my user I don't see that group in the list of my groups.

You are probably joined to that group with your cellphone with a different user account that the one you are using in the web, go to your profile and make sure you have set there the number of the cellphone you are receiving messages in. If not, try to add it, and merge the accounts if GeoChats offers that.