JHB I feel for you, how you were treated, that's pretty shocking, especially for something as weak as codeine. Codeine is a weak opiod and withdrawal shouldn't be too bad at all. Try using immodium (in the states some call it OTC methodone). It will help ease your physical withdrawal (if you still have any that is) the rest is (mainly) psychological.
Take something non addictive but effective for your headaches instead. The Adco-dol was likely making them worse and more frequent in the long run.
http://www.youtube.com/watch?v=2pj9g1FEknM
Here's a video on how to stop opiod withdrawal with OTC items. Take the video with a pinch of salt for a weak opiod like codeine. I'm sure you'll be fine with some good food, vitamins and some damn TLC!
I've come off high doses of Oxycodone with OTC aids for periods of time and it really isn't that bad at all - a bad case of flu at the most. But I'm not an addict, I stick to the dose and don't abuse my meds.
A hospital Dr once told me that codeine was a swear word with him lol. It's really despised by some Dr's.
All the best and good luck.