Costco ATT is such a nightmare

TLDR:
1. I was given a wrong quote (the total extra amount I would have paid is $1500) over the contract
2. I spend probably 10 days going to various costco's, phone lines, and stores to get back the credit.
3. I dont like my phone, so I called for exchange. However, again the same exeperience. first 2 times, the agent said they can not do anything as this Just ATT (or Just Costco) helpline. The last agent said you have crossed 90 days mark. But in reality, I had started the return before that in Costco shop, and it was Costco agent who asked me to call the helpline after he tried unsuccessfully for 2 days. Now I have to keep the phone I dont like for 3 years because of 1 day delay (which was caused by Costco).

What a nightmare!