Hi Sigma,
After four years I would have expected a little more than 2ft of growth.
My advice would be to dig them up and start again.
By virus free certified stock of a named variety from a reputable source, try the major catalogue companies that sell veg seed and fruit you can find them through a Google search.
If you want to look an excellent book before you start again I highly recommend The Royal Horticultural Society Fruit & Vegetable Gardening by Michael Pollock ISBN 0-7513-3683-1 page 215-218
Don't accept suckers as a gift produced from someone else’s raspberries as they can sometimes contain viruses which can affect the vigour of the plants.
There was a similar question on Radio 4 Gardeners Question Time last Sunday (23 January) to yours concerning asparagus that had not put on very much growth. The answer was dig it up and start again. You can listen to Gardeners Question Time on the Radio 4 web site.
Happy gardening
The Organic Gardener