How did you lodge your complaint?
I think I've referred a few times here to their official complaints procedure on their website. I've found that any complaints lodged here, no matter how trivial, are acted on fairly swiftly.
When you submit a complaint here you're given a reference/complaint number.
As far as I know, these reference numbers are monitored by Comreg with some sort of action taken if they're not acted upon quickly. For this reason, it's the best way to go. If you don't have a complaint reference number, you're complaint probably doesn't exist.