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I am sorry to learn of this situation. Your contractor is very likely in breach of contract at this point. While most contracts are somewhat difficult to enforce for failure to meet deadlines, if you have a specific quoted timeframe for completion (7 weeks) and the contractor has exceeded this timeframe, causing you documented financial damages (inability to open your store, meaning at a minimum a loss of rent money, in addition to other costs and lost profit), you start having a good claim for the breach of contract I mentioned initially.
You noted that you got corporate involved, often this is a good leverage point for franchisees as the "preferred vendors" get a lot of business by having this status, if they are not meeting performance goals for franchisees, the corporate office can pull their business as a preferred vendor resulting in a much greater loss of business profit/advantage for the contractor than you can impose on them from a single breach of contract suit.
You can also explore the possibility of mediation. Short of filing a lawsuit, you can try to mediate the dispute with them - contact your local bar association and request referrals to mediators, a third party neutral can often help you reach a mutually agreeable resolution. Use the bar association's referrals to contact a mediator or two, the mediator will then contact the other party to set up a mediation session, and you can go from there - hopefully resulting in a formal or written settlement agreement, and save yourself the time and expense of litigation.