Company Pension Issue Urgent

I have been with current company for 3 years and indicated that I would be on their pension scheme after 6 months (probationary period)

Unfortunately still waiting for HR to organise this. I am not getting any support from them and very frustrated. I am wondering what is the best approach at this stage.

I am thinking of leaving but dont want to lost my pension benefits of the last 2 and half years.

Any help/advice would be much appreciated. Have thought to contact a solicitor to push this forward and get some answers..

How did they "indicate" this? In writing (e.g. contract of employment, company handbook)? Verbally? Or this is simply something that happens for all other employees?

Have you tried writing to the Trustees of the pension fund? If this fails can you contact the Pensions Board for advice?