Issues with O2 refund

[GMac11]

Has anyone out there had issues trying to get a refund after leaving O2?

I upgraded my O2 refresh contract and paid £49.99 up front for a S7E but cancelled and returned a few days later (well within the 14 day cooling off period) and left with my PAC to Vodafone for a better deal.

This was a month ago and I have been on to O2 several time either by phone or Live Chat and have been promised my refund every time, including an extra amount as a gesture of goodwill (the latest interaction was last Thursday) and still I have nothing.

Any advice on how to get this rectified?

 

[GMac11]

It's not even a case of them saying they won't refund it, they said they will but what they say and do seem to be two different things at this stage.
Also, unfortunately going instore is no good as it's one those situations where the Retail arm and online arm are conveniently separate entities.