TAN/TCS Issue.

dear expert.
we are a private limited company dealing in timber having registered office in delhi. we have no business activities in delhi (only book keeping) but all the sale purchase is done in mumbai (branch). now we have a TAN number issued at Delhi and we have been deducting tcs of parties on the same tan number while making sales from mumbai. do we have to apply new tan for mumbai or we can deduct tcs on delhi tan and accordingly keep filing our return. and if we were doing it wrong what should we do now?..please suggest. thank you