Sorry, head not on straight this morning
I still don't think he can do so unilaterally.
I think it is worth enquiring after the agreement to confirm that it is now in single name.
At the end of the day you cannot be expected to pay more than you can afford and loans etc are not priority debts. Your life, your home and your kids come first, whether they like it or not.
I would take a trip to the CAB for some more detailed advice. If you have people harassing you at your doorstep then get trading standards involved. This is what they are for.Until then, and if you get any more callers, practice the line "I will not talk to you, go away", then slam the door. Ignore the threats and "if you don'ts". If they don't go, call the police. There are very good laws to protect you from this sort of harassment.
There are a number of goverment funded debt advice lines that give free advice. Conmankiller usually has the details to hand so if you're watching, can you post them up. If not, I will dig them out.
The important thing right now is not to sit at home in fear of the next knock at the door. There may be legal avenues but these are more stressful and, I suspect, not what you want.
Most important is to go forward with your eyes open as there are pseudo legitimate companies out there that prey on people such as yourself. Make sure you understand what is being put in front of you and, if not, walk away and think through any proposal.
Hope this is more helpful (and accurate!) than my last post.
S