No honor

Im not sure where to post this. Its regarding bundled service. I placed an order online, the promotion was was $120/ month plus taxes for 24months. They installed and the 1st bill was for over $450. I've spoken to 6 employees, one had the nerve to say the promotion ended (in one week!). Both supervisors Fran and Jennifer told me they would correct, but I'm still going to have to pay upfront and they will discount later. They refuse to honor the contract and if return the equipment my credit will suffer because i do have honor the contract. Please help me!