Promotional Trade-In Credit Never Applied to Account?

I am seeing a similar scenario. We traded in my husband and son's phones when switching from sprint to T-mobile. We were assured that the trade ins would be accepted but that the trade in would not be applied to the account until the phone was received at the main T-mobile branch. I had called to check on the trade ins and was assured the credit would be applied to my account, however, a year and a half later the trade-ins were never applied. The company basically lies and promotes misleading promotional information. We could have sold our phones on our own and received the money, but instead this very corrupt company took our phones and made a profit off of our phones and the sale of the over-priced phones. I will be paying my balance off and switching carriers. I will be filing a complaint with the FTC and FCC. This company needs to be investigated for their misleading information and corrupt means of managing business.