Ticketmaster sold me a type of ticket that they then didn't honour on the day of the concert. I received no communication from them prior to the gig informing me of the changes.
The tickets I got were worth less, but they are only offering to refund the difference to an old bank account of mine that I no longer have!
I have asked them several times via their digital chat where I can raise a formal complaint to to get my refund and they keep avoiding the question!