0% Ending

Hi - please help, I don't have a clue what to do!

I have just under a £3,500 balance on my barclaycard platinum - it is almost maxed. I balance transferred £1000 initially on an 18 month 0% deal which is due to expire in 5 weeks. I had all good intentions of paying it off in full before the deal expired but life changed and I got in to some difficulties meaning I had to spend on it whilst also incurring current account bank charges which have severely harmed my credit rating. Over the majority of the 18 months I have been managing to pay at least the min payment - none missed. The trouble is that in 5 weeks the APR will spike and I do not have the ability to get another 0% transfer card - I have tried but only likely one is the poor credit one that allows only 0% for a short period with £1500 limit. The repayments are going to be too high for me to manage on £3500 at full APR.

Is it at all possible that barclaycard would extend the 0% deal or reduce the APR without having to default?!

Many thanks for your help.