offer of rebate that disappeared during the rebate process

I have signed up for Time Warner cable when I moved to a rental house in July 2016.
They offered me a rebate of $300 gift card if I choose higher priced package and keep the package for three months, they will issue me a $300 gift card.
I suckered into a higher package and had it for almost a year now.
I realized it has been almost a 10 months and I have not seen any gift card.
I just called the TWC to check the status.
after 3-4 different department, they told me they no longer has a rebate program. They can't give me a rebate gift card.
I filled out all the paperwork, got an email confirmation it will take 3-4 months to process.
It is not the gift card but how they just ignored the promise they make to consumers to their convenience.
I thought they should honor the offer because the offer was valid when applied for it. It is not the fault of a customer if the company decide to end the offer during the process.
I am very disappointed at TWC. Never again
Any other customers out there, do not buy premium packages on rebate promise unless you really need it.