If you do want to take them to court you may have the option (dont know what your contract looks like or what addendums are there) to sue them for specific performance which means the courts would force them to perform on the purchase agreement. I would highly recommend an attorneys opinion before considering this option.
Our realtor has been attempting to get in touch with the buyer's agent for almost a week now and still has received no actual phone call back. Is there anything we can do or just leave it in our realtor's hands?
We're just concerned about paying two mortgages until we can sell it and we need the thousand dollars to at least cover next month's mortgage on our townhouse.
If the Buyer won't sign the Cancellation because of the $1000, do you really want to tie your house up over that small of an amount? It likely won't even cover one house payment...
If they are unreachable and that is why they won't sign, you'll need to get a Statutory Cancellation from the courts.
As always, I am not an attorney and you should consult one for legal advise.