Verizon's arm twisting

I've switched from DSL to FIOS service with a commitment from Verizon that they'll convert the old service into the new one and accordingly verizon activated my FIOS triple play on Jan 4, 2008. Though I recieved a payment request for the DSL in the 2nd week of Jan 08 but since the installation happend only on 1/4 presumed the same will get adjusted in my future bill and paid fully on 1/20. To my shock they sent me a bill for Feb 08. After spending almost an hour on phone reached a customer care agent and they've asssured me that everything was taken care of and they'll send me a credit. As anybody I trusted that individual. But what to say about an organization when they keep on sending invoices after all these assuracnes. Since I didn't want to spoil my credit history talk to their customer care department again in Apr 08 and they've reassured that the excess amount that I paid will be credited back and also that no payment to be made. Within 2 weeks of that call I'm getting threatening mailers saying that they'll proceeding with some collection actions. I don't think anybody can save this company. I've not seen any cheats like Verizon in my life.