IF you've missed enough payments then I think they are within their rights to take it away but if you are offering to pay something then they do have to consider it. I don't think that actually means they have to accept your offer though but trying is better than burying your head in the sand.

Call them and keep asking to speak to someone higher and see how you go. Keep asking to speak to their supervisor if they tell you no. Be nice, polite but firm.

I would think that if you're at least offering to pay something even if it $20 a week they might accept that and it might be enough to keep it. I'm sure you can find $20 even if it means you eat spaghetti on toast for the next month

Maybe you can go through your stuff and have an ebay sell-o-rama to raise a bit of cash to put toward it...

At the end of the day though you should be prepared for the worst case scenario so back up everything JIC they repossess them.