How to get a contract nulled

Contracts are meant to be binding unless you can prove fraud, misrepresentation, failure of consideration, or material breach of the contract.  You each have made a binding promise to the other: you will pay the 4 monthly installments, and the contractor will plow/shovel whenever the snow is in excess of 1".  One inch is a standard trigger in these sorts of contracts.  The fact that you have to wait your turn in line for the service to be rendered is also not unusual (unless you have paid for priority service), so long as the service is rendered within a reasonable period of time after the trigger is met.  Therefore, if snow removal occurs within 12 hours of the trigger, this would be reasonable.  If you are waiting days for the service to be rendered, that is a "material breach" of the contract.  You should document the performance: take photographs of the area to be plowed before and after the services, and create a timeline of events.  If this evidence supports a material breach of the contract, you should immediately put the contractor on notice of the material breach and advise that you intend to cancel the contract on this basis unless they "cure" the situation within the next 10 days and consistently perform as promised.  Then document their services or lack thereof moving forward.  If again, there is a failure to cure or another material breach, send the contractor a certified notice of cancellation based upon the material breach and failure to cure (spell all of this out in your letter), tell them they are no longer authorized to come onto your property to plow, and advise them that you will be contracting with someone else to perform the services.  Pay the contractor all fees due up to the date of the notice of cancellation, and refuse to accept services from the contractor after that date.   If you have to pay more for these services from another contractor because you are not hiring them for the "season", you could sue in small claims for that difference from the defaulting contractor.  Good luck, and make sure you hire contractors with good reviews online.  

A good first step is to review the contract for any termination clause, notice requirements, cure periods, service standards, or weather-related exceptions. If the contract says the company will plow at 1 inch of snow and clear the parking lots, lanes, and available parking spots in a workman-like manner, repeated failure to perform may potentially be a breach of contract. But whether you can cancel right away often depends on the language of the specific contract, your state law, and whether the landscaper has to be given written notice and a chance to fix the problem.