My left earbud isn't working!?

Ok befor u day buy new ones these are justbeats they cost 80 pounds, and this happened to my old ones of the same kind had to replace them with new ones (return policy). Ok so my left earbud only works if I move it around, had them for about a month :((( how can I fix this? And also can I replace them with new ones again, I need a quick fix! K bye btw I need a techie to tell me something