It sounds as though you have taken them off the plant too soon. Personally I would just compost them and take it as a lesson learnt. What you should do with runners is keep picking them as long as you can and then when they start to grow slightly deformed on the plant, that is the time to stop picking them. The ones you leave will then develop large beans in the pod. Don't touch them until they dry a little and become brittle. Remove them from the plant at that point and then hang them in a onion sack, somewhere dry. Leave them there to dry and they will be ready to use when they look like shiney shells. As a rule they will be purple and black. We then soak them in water overnight before removing the skin from the bean and then adding them to vegetable soup. They are without doubt, the highlight of the soup. Well worth all the effort !
Keep some of the dried beans back and these can be used to sow next years crop. One more thing you should consider.. When your beans have been producing a crop for 6 weeks.. Plant some more, these will carry you right through until the first frost.