Hope this is the right place to post..

I got in a 24 month contract with vodafone at the end of 2013, at this time I had a job, a couple of months later my job went into liquidation, it was a bar job, My only income and during this time I was also depressed as I had someone close to me in hospital who passed away. Anyway I couldn't pay the bill and each month it was going up. Then Vodafone transferred it to Lowell or someone before that.
So basically I owed £792.88, I'll admit I ignored a lot of the phone calls and letters as I had no job and didn't know what to do and had a lot of stuff on my mind, now 3 years later I have received a claim form from the county court business centre in Northampton from Lowell which says I have 14 days to respond.
Total amount is 922.88 including court fee and legal representive.
I'm self employed and could only really pay back in instalments of £15 a month atm which I know they won't agree to as would take years.
I tried to contact them before and each time it's been unhelpful.
I really have no idea what to do or how to respond to this letter, is it genuine? And what should I do? Will they let me pay in instalments or is it too late now? I'm in my 20s and still live at home.
Please help!