Probably the quickest way (excluding any queues you'll have to wait in, of course

) is simply to escalate your call to a manager.
Now, at first any advisor will escalate to a coach - who have limited abilities to resolve - however, you can stipulate that you wish to speak solely to a manager, and yo'll receive either a transer or call back. A manager, in all honesty, can rarely be bothered to argue, and offer a 'gesture of goodwill' (if of course your complaint can be remedied with a financial payment). I have also known some calls be escalated to the Call Centre Manager, so my advice is to hang in there - i know it can be time consuming, but you can certainly resolve your issue with one call. Just keep escalating.
If you want a bit of specific advice on your complaint, PM me and i'll offer the best advice i can.