Is my iPhone lightning port damaging my cable?

I have an iPhone 5, iPod Nano and an iPad that charge with lightning cables. I have run through 3 Apple cables and two generic cables, all showing the same signs of wear on the lightning pins, all of them on the same pin.

I have read many discussions about the corrosion of lightning cables and how people says that Apple should fix it, but I haven't found any discussion that says WHY this happens. Why is it always the same pins on different cables that burn out?

My logic says that an external factor is placing strain on that one pin and I am sure that it is the lightning port on my iPhone that is the culprit. Unfortunately I'm a woman and when I speak to Apple personnel about my problem they talk down to me and say everything that I've already read without actually answering my question. I asked whether it could be the port, but the guy just said that because it charges on their cable, there's no problem with my port.

That's not the point, after several uses (or two on my last cable) the pin start discolouring and eventually stops connecting. This happens every time even with a brand new cable. Should I really keep on buying new cables every two months or can I find the root of the problem and fix that?

Can someone PLEASE tell me if it is a faulty lightning port that is causing this problem? If so, I can just have that replaced.