Package deal prices do change from month to month, and year to year. Sorry, that's just the way the business is, no matter what cable/internet provider you go with. You may pay more than your neighbor, simply because the company had a "special offer" going on, when he or she signed up, that is not available now, but may be available later--to new customers, usually. Them's the breaks, I'm afraid. You could just wait until a one of these deals comes along, or ask if they have any "special offers."
As far as the customer service complaint, that is something you should take up, either with your state's public service commission, or your state's attorney general's office--or both, if you feel strongly enough about. Let's face it: the only way to solve your issues, is to start the ball rolling yourself...which you began with this website...up to you whether you want to follow through or not.
Also, some phone companies offer internet service...and you are NOT forced to choose only one internet provider, in most cases, as long as you have a phone line. If Mediacom is telling you this, they MAY be lying, and IF they are, they are probably breaking a state or national law.