If after reading the available literature you feel you should make a complaint and possible try to seek compensation for your mis-sold endowment policy, you should first of all speak to the company who originally sold you the policy. If this company doesn't have a formal complaints procedure or you aren't satisfied with the procedure itself, you may want to speak to a specialist claims compensation firm.
You should be receiving regular projection letters showing whether or not your endowment policy is on track to repay your mortgage. This letter may inform you that your endowment mortgage policy may not reach the required total amount to pay off your overall mortgage loan. If this is the case the FSA are the best place to contact to decide whether or not you need to claim endowment mortgage compensation from a third party firm.