If there is any confusion about your terms, bear in mind you have a legal right to receive a written statement of particulars of your main terms and conditions of service, and for that document to be kept up to date. Speak first of all with your immediate supervisor. If you do not receive a satisfactory answer within a reasonable amount of time then you may wish to raise the issue with a more senior manager.
If you are not satisfied with the answer from management or you do not receive one, you may wish to take out a formal grievance in accordance with the provisions of your organisation's grievance procedure.
The ACAS Code Of Practice on Disciplinary and Grievance Procedures provides guidance on how employers should address grievances. You can find a copy of this document on the ACAS website (PDF download).
If you are a member of a trade union you might also wish to raise the issue with your union representative.
