If the problem is rate control, I wonder if it's time to do an AV node ablation and go to permanent pacemaker.
p.s., there's a new procedure in the US called a 5 box mini maze. It has shown some promise for persistent AF. I'm guessing you're int he UK, not sure if they're doing the procedure there.
I feel your pain! I went through a-fib for 14 years. Had 3 ablations, more cardioversions than I can count, and felt like you do. Had to work, always exhausted, etc. After the 2nd and 3rd ablations made things worse, I insisted on a second opinion medically. MY ONE regret is that I didn't do this sooner. As I'm sure you know, when you have this going on all the time, you aren't thinking much further than getting through the next episode.
I was referred to a cardiothoracic surgeon who worked with my electrophysiologist cardiologist.
I had a bilateral thorascopic surgery, similar to 5-box on December 12, 2012. My 2 weeks off work turned into 7 weeks as I developed pneumonia and was very very ill. However, since my recovery, I have only had one minor episode (45 minutes and it self-converted) of a-fib. This was at 17 months. I am now 21 months with only this one small "blip" on the screen.
I continue to be mindful: no caffeine, limited chocolate, watch the sodium, stay hydrated, and take a diuretic once a week. I exercise regularly 4-5 x a week, eat healthier than ever, and feel like I've been given a second chance at a good life. My job is highly stressful (I work with mentally ill heroin addicts on methadone) so I have reduced my hours to 32 per week. My "blip" happened during a particularly stressful time at work when my hours had crept up to 38 per week).
I really encourage you to find a cardiologist who takes your condition seriously. It is always okay to get a second opinion. I'm not sure where you live, but there are many fine clinics available, and it is well worth seeking out the best care you can find. As I said, my one regret is not getting a second opinion sooner. GO for it! There can be life after a-fib.
Sending prayers and hugs for you to have peace and health soon,
MaryLL