You say your neighbours says it's no longer the cultivated rose variety but what do YOU say? Did the flowers resemble those of the Dog Rose or did you find you had two varieties? As has been said, roses are usually grafted onto dog rose stock but sometimes suckers spring out from below where the cultivated variety was grafted on. If you can see the graft (a bulge just above soil level, and if there are branches coming out BELOW this graft, PULL them off from the main stem. What is left will be the cultivated variety. From mid-February onwards, but not when the ground is frozen, prune the entire bush. Now you can do this two ways - prune to say 3ft from soil level above a bud this year, then down to 6" to 10" next year, alternatively go straight to the 6"-10" in one go, a bit risky but it should work. Use clean, very sharp saw, loppers or secateurs, then feed the rose after pruning. Lots of lovely horse muck and if it's fresh, leave a 4" gap around the stem. Before anyone leaps in with the old fresh v well rotted argument, I've 90 roses and have never ever burned one, and they all trive on both fresh and well rotted horse muck.