TDS Deducted by Party but NOT depositing in 26AS.

I had provided services to a company. They deducted TDS and some extra amount and paid the balance. But, even after repeated requests / emails, they are not paying TDS in I.TAx in my account. Now the party is not lifting the phone also. Please inform if writing to I.Tax authorities can help? Which I.Tax authorities should I approach? Sending relevant documents with ITR to Bangalore for verification will help? Please guide.