Repeating what others have said but driving ONE POINT HOME:
Get advice before accepting responsibility.
First, go to the CAB and get them to speed.
You need to find out where the notices have gone. If this is a property, they would have been sending notices to be included in electoral lists, as well. Someone was receiving this and either binning them, not forwarding or possibly giving false information.
I would go as far as to say if you were paying rent and someone was collecting saying "everything included" and you can show paying no other utilities, it may, in fact, be there responsibility as a "landlord" subletting a space.
You may discover that someone was falsifying information
You need to get to the bottom of why you received no notices. If a property is two months behind, it is automatically escalated and keeps climbing.
If, in fact, you become liable, they may even make a token payment.
And if you are found liable but feel that you were deceived by someone else not forwarding information, etc, or making assumptions on your part, you may be able to take them to court to recover.
But deal with it asap. Start with the CAB but don't enter into any agreements until you get to the bottom of why you never received any bills.