Missold interest only mortgage

We were offered an interest only mortgage in 2009 when we were struggling with debt and had an IVA in place. We've paid the same interest rate since 2009 and our property is now in negative equity. We have no savings and cant afford to pay any more money each month to pay off some of the mortgage. Im very worried about what will happen in 6 years time when it is up. Now Nram has sold our mortgage to s finance company. Claims company has said we could have been overcharged but im not willing to sign anything as they want a credit agreement put in place. Financial advisor says the only way out is to pay more monthly. Any advice gratefully received.

I guess we were hoping that the house prices would rise enough in time to pay our interest free mortgage off with the proceeds of the sale. Sadly were now in negative equity along with a short lease so we need to find 3.000 to extend it. Not in a good place right now.