the 307 is fast becoming a nightmare. There are a few posts on this forum concerning the suspension,some people have had just about every part replaced to no avail. I would take it back to the dealer and ask to speak to the head technician/service manager and point out your concerns forcibly but politely (just now).davey102001 said:
The steering sounds as though it is either out of alignment or the steering wheel has been fitted out of alignment.
The suspension could be suspension bushes,upper suspension strut,anti roll bar,axle bushes. The upper suspension strut/link can have a bearing on wheel alignment as well,maybe kill 2 birds with the one stone hopefully.