You can find good advice about
when and how to cut hedges on the
DEFRA site - this is the advice that most councils adopt.
Do you have a Parish Council? These smaller bodies are often easier to deal with, and they tend to know their local areas better. They also have pretty good contacts with the local council so can often get results for you OR point you to the right person.
Failing that I'd suggest you put your case in a letter:
telephone first but then follow up in writing. You can also visit your local MP's surgery if you feel that the council are avoiding their responsibility. Do double check your facts though about what you can reasonably expect the council to do - try rummaging around on their website as they'll usually provide pretty up to date information about hedge and roadside maintenance (and cutting schedules).