Monitor replacement

Who do I contact or call to get any real replacement done? Dell has refused to dispatch a replacement monitor for my replacement UP3216Q and the most recent service request chain started on September 3rd. I've wasted too much time trying to get support to do anything! 

I used to own a UP2715K. After it went bad, I had it replaced under warranty on June 3rd. 

UP2715K replacement came with a stuck pixel. This was replaced, but they ran out of UP2715K so they sent me a UP3216Q.

Replacement UP3216Q had a stuck green pixel. This was replaced. 

Another replacement UP3216Q came with huge uniformity issues. USB hub was also bad. This was replaced.

A third UP3216Q was sent. This one also had uniformity issues in backlighting. A return label was created for the 2nd UP3216Q and the 2nd 3216 monitor was shipped and received on Sept 7th in Houston after some delays by hurricane Harvey, signed by a WALKER, according to UPS.

Since then I am stuck with the 3rd UP3216Q, which has yet to be replaced because Dell thinks this is fraudulent but they've been shipping me panels which shouldn't even pass QC, especially for what >$1000 monitors amount to and what I've paid for a UP2715K. They claim they haven't received the 2nd UP3216Q and everytime I've emailed or called, they wanted a combination of 1) invoice 2) picture of service tag and then I get a reply that it needs to be cleared by the back end and it'll take an additional 24-48 hours.

After which, if it happens in 24h at all, is they need further proof and it's still not cleared yet. I contact again, same story.

Who do I contact to get this fixed IMMEDIATELY? I'm sick and tried of this *** and my patience has run out.