What exactly you mean when you say you have a "Company"? Is it a Proprietorship firm?
In any case, the GST number of one firm cannot be used for another firm. Each firm need to have distinct GST Numbers. You may consult your local GST consultant in this regard.
You cannot use the GST of a Private Limited Company which has a distinct entity of its own besides its Share Holders and/or Directors. Similarly, a Partnership firm is a different entity where there is the possibility of overlapping of individuals as Partners or Directors.
You may consult your local GST consultant in this regard.