If you are a union member you should call on their help. You can also approach the Pensions Advisory Service (TPAS). This is how they describe themselves:
"We are an independent voluntary organisation that is grant-aided by the Department for Work and Pensions (DWP). We provide information and guidance to members of the public on all pension matters, covering state, company, personal and stakeholder schemes.
We also help any member of the public who has a problem, complaint or dispute with their occupational or private pension arrangement. We do not deal with problems, complaints or disputes relating to state pensions. Our service is free and is provided by a nationwide network of volunteer advisers who are supported and augmented by technical and administrative staff based in London.
We are very proud of the calibre of our personnel. Our volunteers and pensions technical staff have many years experience working in the pensions industry and have a wide range of professional qualifications."
You can find further information about the services TPAS provides.
If you have a case, TPAS will try and reach a settlement through negotiation. If this does not work, you can take your case to the Pensions Ombudsman. You will need to fill out a form that you can get from TPAS. In general, you should contact TPAS before you go to the ombudsman.