The IRS kept my refund

I received a letter from the IRS stating that I had to provide verification. That my two son’s were full time college students. I then provided the tax documentation from their colleges and other supporting documentation and faxed those documents to there office two times. I then callled almost everyday and was on hold for long periods of time to no avail. I’m unable to reach the IRS by phone or via mail or fax. What should I do next in order to receive my $6,000 refund that they owe me?