Unfortunately you agreed to pay a cetain amount over a certain number of months and Orange could hold you to that if they wished. You could offer, for example, to pay the £299 at £5 per month over the next 60 months. You need to compare the cost of cancelling with the cost of continuing both as a total and as a monthly amount to see which is best for you. It is for you to discuss and make offers to Orange and it is for them to decide how much they will help. Obviously they will not want to take court action against an unemployed person if they can see an option that is better for them.
You can also ask around to see if there is a trusted family member or friend who would be willing to take over the phone. If doing this though, you need to realise that the contract would still be in your name and you would be ultimately responsible for the bills. You should only consider this option with someone whom you trust.