as my post states. the one exception for shoddy work at a retail price only comes from a retail store. you are not the first victim of these retailers that hire sub-contractors. This "installer" as you call him is a sub-contractor. as such he is required to carry a liability insurance policy that covers problems like this.
1. Call a lawyer.
2. have a seperate contractor properly repair and install a quality countertop.(which will leave you very little downtime in your kitchen because he can take his measurements with your existing countertop installed and rapair/relace all necessary materials in one day.)
3. Have your lawyer file a claim with the "installers" insurance company to cover the costs of repair/replacement and maybe........?pain and suffering?
sounds like you have a good case to me!
If you choose not to call an attorney, then live with what they offer and peace be with you.