There is surgery, and a number of options. However, it may be that your local PCT don't fund them, as I have got the same issue. I was diagnosed with overactive bladder, although that diagnosis changed recently to urethral stenosis. My only symptoms are frequency, like you I go around 20 times a day, although I am very fortunate not to wet myself, and generally don't have too much of an issue at night.
I presume you had the urodynamics, and from they gave you a diagnosis? They should really be booking you for a cystoscopy where they put a camera in to have a look, and often dilate your bladder as well to check its actual capacity. It could be you have something called institial (probably not spelt right!!) cystitus, which has very similar symptoms to overactive bladder. However, they need to see inside your bladder to diagnose that.
Medication is often the first step, I have tried all sorts, but not vesicare I don't believe. They may also consider bladder retraining and dietary changes, as certain foods/drinks can irritate lining of bladder.
There is medications that can be inserted via catheter into the bladder which help coat the lining and stop it from being irritated and therefore control the frequency. These didn't work for me, but often do.
Surgical options include botox injections, but as I said, not PCT's fund these. I asked for a second opinion and was sent to another area, and due to that have now been put on the waiting list for the injections. There are other options if these don't work.
I have been seeing various consultants on and off for 20 years, and have been fobbed off a lot of the time. What I have learnt this year is that if you're not happy say so, and that you have the right to ask for a second opinion, and you can also have some input into this. I googled the institute of urology in London, and on there is a list of consultants who are both private and NHS, and what there specialisms are. I chose 2 of the NHS ones, and told my consultant (who had told me there was nothing more he could do because botox wasn't funded) that I wanted to be referred on. He said I had to do this through the GP, and they were quite happy to do it through the choose and book system.
Anyway, good luck, and keep perservering, plus you never know, the medication may actually work which would be fab!