What is the best way to grudge a consumer complaint in the UK regarding non-delivery of goods associated with the sale of a concert tickets?

I ordered two tickets for a concert that took place on Feb 7 at the O2 (Indigo room). I purchased more expensive tickets because they included a laminate and programme souvenir. Those were not made available by the promoter on the day of the concert. We were told they would be sent. Weeks passed. I contacted the venue and the promoter, and I was told that they would be sent. Months passed, and nothing. In the meantime, I contacted the various parties again, but this time no answer. I would like to get what I paid for, or else get reimbursed for it. Is there a consumer agency that offers mediation between consumers and merchants the way there is the Better Business Bureau in the US?