Iphone 6 data cable problem

HI i bought my iphone 6 march this year and by april i had to replace the data cable because my phine wouldnt charge because the 2 middle contacts on the cable had seemed to of burnt the same thing happened again in july to the new cable so had to buy yet another cable and now a month on and the same thing as happened again to the 2nd new cable what is causing this to happen