You can sue them for breach of contract (not providing what they agreed to provide and for which you placed a deposit) in order to recover your deposit; you are unlikely to be able to get them to pay for windows from someone else unless you can show due to the delay, you suffered some additional economic harm (e.g. windows went up sharply in price); normally, in cases like this, your recourse is to get your money back. If the amount falls under the maximum limit of local small claims court, you may be able to sue in small claims to save the cost of an attorney.