Upgrading plan - not getting price as promised

I am a existing customer to the Gainesville (352 area code) area with Cox. Sadly, they have not honored the price promised when upgrading the service.  I've been on the Internet Starter 10 Mbit plan for 19.99$ for some months. I called in to inquire about faster speeds and was upgraded to Internet Essential 50 Mbit for 29.99$. They guaranteed that I'm able to upgrade into this 29.99$ plan without issues and that I could go back to the old plan if I would want at a later stage. My bill now shows close to 47$!!! I called in again and was told there is nothing they can do. They won't bring me back to the initial 19.99 plan as the promotion is no longer "valid". They also refused to honor the promised price of 29.99..

Thats 50% more than the promised price..what a ripoff.