Unhappy with customer service

I have a Samsung galaxy note 4, screen had to be replaced, after a quick and painless ADH claim, where as promised they picked up the fone, left a loan model exactly the same, upon return of my old device i have noticed the phone wiffi and network to be very poor, as we are 3 in the house with the same fone and network, and 5 in the friend circle, i have compared with them, there is a huge problem, i have though it to be the reset done on the fone, therefore did another, and a software upgrade, none of above mentioned worked, i have contacted Samsung in regards to my problem through the contact us page, no support has been given, i also have tried to see if i cannot just book another ADH as I cannot battle like this, according to the App my status is expired.