Hi Connemmara,
A few questions need clarified here, when did you start getting the "red letter's"? Most companies were dealing with this some years ago and you should have had a window of opportunity to get back to the company with options they may have provided for you. Were you aware of the risk involved in having an endowment to repay your mortgage? Were you aware that the endowment may not pay the mortgage in full?
There are companies that will offer you a part interest and part capital repayment giving your circumstances and the fact that the endowment may not pay the mortgage, and this can be done to after normal retirement age, provided you have the income to meet the repayments, so it will depend on your income, the amount outstanding and the value of the property. You may also feel that you were unaware of the risk involved when you took out the endowment and possibly ask for the plan to be reviewed.
I have just registered on this site and I am not sure if you can get access to my Email as this is my first ever response, but I hope this helps as I am a Financial Adviser. I would normally leave my contact details but I am unsure whether this is wise on this site as I said I am new.