Availment of CENVAT

We are a manufacturing company having Excise Registration (under SSI Exemption). We have opened another branch for the same activity on a different location but on a much higher scale with imported machinery. We imported the machinery from Germany but by the time the machinery arrived our Factory Building was not ready and hence we could not have EXCISE registration for the new Unit. When the Building was ready we applied and got the Excise registration and the machinery were installed and the CENVAT (CVD etc) was availed in the first month (50%). However, the Excise Department is objecting to availing CENVAT on the machinery purchases made before the registration date. The CENVAT Rules are silent on the date of registration and availing CENVAT.  Please let me know the correct position.