I've shopped Amazon, but never had to return anything. I did order a book one time that seemed to take forever to ship (like 3 weeks). It wasn't with Amazon prime but they interacted with the vendor on my behalf.
I haven't had any issues returning items to the Q, but sometime it takes for ever when you use their labels, I think because they use parcel service which can be be extremely slow. I am tracking one now which was given to my mail carrier on 1/6. It is still in transit 10 days later and was last updated yesterday. (I live only about 5 hours away.)
You need to call your postmistress back and tell her to listen to you. You are not giving her a USPS tracking number, you are giving her the Q's tracking number and it should have been scanned in. I am not sure exactly how it works but Q has a parcel return service with USPS either of them should be able to track if it was scanned.