Terrible experience. I bought a refurbished iphone...

Terrible experience. I bought a refurbished iphone 7 about 4 montha ago and the sound when calling was terrible that the only way for people to hear me was with headphones. I complained but was told to do a hard reset which didnt help and never got a reply again.
I gave it another chance and this time bought a prestine condition iphone 6s and the charge lasts 10min and takes forever to charge. I complained and was told to do the same. Hard reset which does not work. I am still waiting for a reply of how to get it exchanged.
Do not buy refurbished phones as the garantee or 28 days money back does not work. It seems to be fake