Five month billing decrepancy

Upgraded my iPhone 7 Plus in July to iPhone 11 online. Was told I would receive packaging and labels to trade my old phone in to receive discounted payments on the new phone.  No packaging was received so I was told to take the phone into an Att store which I did in the LaDera Center in Los Angeles. To date five months later no discount on my bill just endless excuses regarding the number of billing cycles it would take to become effective.  Called again today to inquire.  Same old song and dance. Instructed to call some specialized department.  I refuse to keep playing these games with you guys. Covid gives everyone an excuse for shoddy customer service these days.  You will soon be looking at an ex customer after over twenty years of patronage, but enough us enough.