Missold endowments

I am sure this may have been covered before, so upfront apologies for lack of searching!

A good while (a few years) ago, I complained about a missold policy, and this was rejected by the company, and I basically didn't pursue.

For two reasons I have regretted this:

1. It was a clear 'it will give you the amount plus profit' case
2. The financial advisor who sold it to me is no longer in business, neither could he be found.

Have I forfeited my chances of having another go at this through the time expired rule, or is there any other route I could try?

Thanks for any thoughts - good or bad!

Mark