iPhone 6 - charging port problem

Hello. I have iPhone 6, a few weeks ago i’ve decided to change charging port, because charging every day was more difficult and cleaning was not helpful. I bought one on marketplace. When i’ve changed it, i noticed, that signal is very poor and sometimes was no service, and baterry was dripping very fast. On original port it was okay, when i’ve change it again. I bought another one, and i had the same problem. I decided to use my iPhone like iPod, but a few days ago it charged to ~10% and stopped. iPhone see charger, but won’t charge. Then it turned off. Now when i plug charger, iPhone doesn’t react, there is only black screen. But sometimes when i reset phone several times (hold home and lock buttons for 10 seconds) it charge and turn on, but charge only to about 5% and stop. I changed port few times beetwen first from marketplace and second (original don’t work anymore) and i have still the same problem. I want to buy original, used port from someone on internet, but i’m not sure that problem is with port or phone and i don’t want to lost my money. Thank you for every answer and sorry for my english, it’s no my native language. :)