you need to contact the adviser who sold you the policy. this may or may not be the company that the policy is with, but they need to be your first port of call. They will either investigate your complaint or tell you who the adviser was and pass your complaint to them. The majority of companies now time bar complaints, this is based on the date that you first received a red letter, so if I were you, I would contact them asap.
Whether you are entitled to compensation or not, depends on your reasons for complaining and the evidence available to back this up. For example , was it made clear to you that the policy may not pay enough to cover your mortgage?, were you promised a lump sum? Does the term go past your retirement date? Did you have any requirement for the life cover? If you are purely complaining about the performance of the complaint, you will not be entitled to compensation. Companies are strictly regulated and have a duty to properly investigate your complaint. You then have the option of going to the Financial Ombudsman if you are unhappy with the decision from the company.
You do not need to go through any of these companies that charge you to help you with your complaint and in fact, a lot of companies refuse to deal with them on the basis that they are not doing anything for you but are taking your cash. All you need to do, is contact the company in any form and tell them that you feel you were mis-sold the policy (for whatever reason you have) and they will then follow the process which has been agreed with the Financial Services Regulator.