You can easily identify a vole's hill if you find roots and other parts of plants in the hill or in the tunnels. Besides, they are not as high as mole hills. A simple test to confirm that you are dealing with a vole is to carefully open the hill. If it is closed within a few minutes, or a time up to six hours, you can be sure this was a vole.
You should abstain from chemical pesticides as pesticides are passed through the food chain.
Voles smell and hear very well, just like moles. That is why we can use domestic remedies which have been proven successful. Voles, e.g. do not like the taste of garlic cloves, thuja twigs, dog hair nor leaves from walnut or elder. So you can place smelly things like that in the entrances of the vole's hill.
Trade also offer appliances which banish voles with the help of sound waves or vibrations. They differentiate in their sphere of influence. Best is to get informed in a do-it-yourself store or specialised garden centres.