Interim updates on Tracker Bonds are sometimes not very meaningful if they depend on the level of an index after the term of the Bond.
Having said that, Mercury should give you more information, especially if they have promised it. Request it in writing and then make a formal complaint which you can take to the Financial Services Ombudsman.
If you search Askaboutmoney for Helvetia you will find some unfavourable comment. However, I am not sure that there is much you can do about your bond if you are not happy with Mercury or Helvetia.