Upgraded iPhone, Paid in Full and Signed 3-year Contract, Do not see the monthly credit on my bill

Read the terms! Monthly credits do not start until the third or fourth billing cycle., if you have met all the requirements. 

No reason to contact anyone yet. Trade in deal credits take up to 3 bill cycles to show, so no credit yet is not unusual. However, you also said in your title “paid in full”. There is no 3 year contract, it’s a 36 month installment plan on the phone. If you paid for the phone already, there is no installment plan and therefore there will be no $800 credit.

So in order to get the $800 credit I have to take on debt?? That wasn't what I signed, I signed that I would pay in full and still get the $800 credit... Does that also mean I'm locked in for 3 years with NO benefit? So this basically just COST me an additional $35 for an "upgrade" that I paid for?

STUPID if true. Lesson learned.

So in order to get the $800 credit I have to take on debt??

Yes. To get any phone deal credit, you must pay for the phone on a 36 month installment plan, not pay up front.

That wasn't what I signed, I signed that I would pay in full and still get the $800 credit... Does that also mean I'm locked in for 3 years with NO benefit?

You aren’t locked into anything. There is no contract and since you already paid for the phone there is no installment plan. Since there is no installment plan there won’t be any phone credits either. So yes, it sounds like you got talked into buying an ATT locked phone along with the $35 upgrade fee.

You might also want to make sure you weren’t put on an installment plan too. We’ve seen that complaint before from people buying from Apple. If that’s the case, you basically are paying for the phone twice, once what you paid up front and again on the installment plan. If that is what happened, Apple screwed up.

So this basically just COST me an additional $35 for an "upgrade" that I paid for?

So basically you bought a new phone from Apple. That's all there is to it. If you went to the Apple store, it sounds like you already knew you want to buy the phone. 

Actually that’s not exactly “all there is to it”. If i had just declined to bring my phone provider into the transaction at all then i would have gotten the phone withOUT the $35 “upgrade fee”. I was charged that because i did the whole “3 years for credit back” thing, which i didn’t even do because i paid in full. 

Lesson learned: just buy the phone, leave AT&T out of it altogether next time. Anything else is confusing and costs more. 

Or you could buy the phone on a zero-interest installment plan and get $800 (less the upgrade fee).

But it wasn’t zero interest. When you look at the details there ends up being about $138 in interest (on a $1099 phone) by the end of the term. Not zero. 

But it wasn’t zero interest. When you look at the details there ends up being about $138 in interest (on a $1099 phone) by the end of the term. Not zero.

Nope, not on an ATT installment plan. Not sure where you are seeing that. If you buy a $1099 phone, your monthly payment is $1099 divided by 36. There is no interest.