Hi tigger blue - the compensation that you received was calculated to put you in the same position as you should have been had you taken a repayment mortgage at the time of the sale. At the point of receiving the redress, you had to decide whether to transfer your mortgage to a repayment mortgage and guarantee that it would be repaid - using the compensation plus the policy surrender value to reduce the borrowing required, invest the money to put against your policy at maturity, or increase your payments appropriately. The insurance company would have paid the fees for you to transfer your mortgage if you wished.
Endowment mortgages often cost less per month than a repayment, so you have had the benefit of lower payments as well as the redress that you were given, unfortunately, you cannot now claim again.
It would be quite a complicated calculation, but it would be interesting to see whether you would still be in shortfall had the compensation been applied to your policy.
The way the redress is calculated is so that you can transfer to the repayment mortgage which you feel you should have been sold at the time. If you chose to continue with the endowment, then that was your choice at the time.
It is easy to say that now, when I am sure that you had a place for that redress money to go when it arrived.
Anyway, I hope that you manage to get it sorted out, but you would be wasting your time both with the company and FOS if you were to complain again.
Interestingly, there was a case recently where a Financial Adviser achieved a ruling where he would be entitled to be repaid the compensation paid to his customer should the policy meet it's target.