Clearly you are going to need to have a discussion, possibly an unpleasant one, with your contractor. Hopefully you had a written estimate, maybe even a contract, with the contractor, that specified the work to be performed. Maybe you did not, possibly you did not have any plans, which would make the entire discussion even more difficult. Remember, the contractor is only obligated to build to the plans, and meet the terms of your agreement. Things get very difficult if the agreement is for the contractor to build the deck WITHOUT A PERMIT, and there are no plans. If that is the case, the contractor may be perfectly within the letter of your agreement to build a deck with footings that are not code compliant, after all if he is not obligated to pull a permit, is he obligated to meet code?
That said, frost heave is caused by a complex relationship between freezing temperatures, soil type, and moisture availability. Certain types of soil are not prone to frost heave even if they freeze solid. For example, coarse sand and gravel does not exhibit frost heave even if it is saturated and freezes solid. Clay does not exhibit frost heave, however silt does, and most people CANNOT tell the difference between silt and clay, and they get confused all the time. Hence the urban legend that clay exhibits frost heave, it isn't the clay, its the silt. You said you have clay, but I am guessing you don't really know the difference. If you have silty soil, and it freezes, you are almost certain to get heave. If the soil is truly clay, you are not likely to get frost heave. It takes an experienced person using specific tests to distinguish clay from silt.
At the worst, if you cannot get the footings dug deeper prior to this winter, you should hire an engineer or soil scientist to test your soil and determine if it is frost heave prone. If so, disconnecting the deck from the house would be a good idea. If not, the entire problem can wait until next summer, when you should have plenty of time to install new, appropriate footings. Bear in mind that if the contractor failed to build the footings to code, there may be other issues with the deck that will also require attention at that time.