@jefazo92,
In the US, a utility like SSE doesn't care who was cooking what. They just want to get paid.
Before you do anything else, figure out how much you can afford to pay. Sit down with bank statements and a calculator and figure out where you can cut and where you can take some cash from, in order to pay the bill now.
1) If they work anything at all like bill collection in the United States, you can probably negotiate in some manner. In the US, you generally have to be straightforward. They don't want to hear your life story. It's more like,
"This bill is for $3,000 which I can't afford. Can I pay you $1,500 over the course of the calendar year?" And then you see what they have to say. It's a negotiation, so always lead with your most favorable terms. If you could pay $2,000 in 6 months, then this opening salvo makes sense. You have room to maneuver.
2) Maybe - you'd have to check the laws of your area (yeah, hiring a lawyer is probably a good idea). In the US, it's more likely that your future wages would be garnished. So if you got a job in a year (or you already have a job), a certain amount would be taken out via payroll deduction until the debt is satisfied. Again, check your area.
If they can take from one bank account, operate under the assumption that they can pull from both.
3) I don't know how credit works outside of the US. But in the US, there are usually set times for when older negatives roll off your account (these would be negative details such as bankruptcies, liens, court cases, and outstanding debts). Also in the US, the amount of time a negative stays on your credit report has nothing to do with any Statute of Limitations. Hence a bad mark of some sort could fall off your credit report but you could still be charged or sued, or you could still be paying.
Yet again, check your area.
And next time, get contact details for your roommate(s) that are as ironclad as possible, and maybe even get their name put on the bill.
Is it unfair the SSE is only going after you? Yes, but since yours is the only name on the bill, yours is the only name they know of.