How to get help for faulty cooker ring?

I have a concept 361e, bought 7years ago. The back left hob has never worked properly eg it has never been possible to adjust the heat,being constantly on full. Now I find it comes on without being switched on,touching the dial can heat it up. I have now taped over to keep it from being used fearing it could cause a fire if something was left on hob. I wish to know if this was a fault in other cookers of this type and what can be done to fix/make safe my cooker. Thank You.
Mrs.M. Dempsey