I would see a professional about permanent laser hair removal. It can be expensive, but it is a good long term fix. In the meantime, any salon that does waxing should be able to take care of it.
You could either wax your back every month or you could go and see a beauty consultant and get the hair permanently removed with laser treatments. It could take a few visits and cost a lot of money, but it will work.
I use a spray on nair. It comes as a foam spray. It cost's somewhere between 5 and 10 dollars at drugstores. Simply spray it on, wait 5 minutes, then shower to rinse it off. You will have to repeat this process once or twice a month for best results.