Q1: - Is it advisable for me to sit in the office premises?
No. It is not advisable, it is unnecessary adventurism and gives another arm to your employer to initiate another proceeding with a fresh cause which will add to your existing troubles. In fact it is illegal. Nothing more to say on that.
Q2: - if i do as asked in above question then can the department stop me to do so?
Yes. They can certainly stop because, the higher authority must give you acceptance. But you can formally ask them to give reasons in writing (you too must ask them to give reasons in writing not orally...handover the letter personally and take signature on the copy of it having received by the authority itself or by the concerned clerk of Tappal section of the department) if they do not allow you to work. If they do not give those reasons in writing you have to write the same in Contempt Petition that despite having CAT order they have not allowed me to join service and despite asking them to give reasons for not allowing me to join they have not given the reasons.
You can go for Contempt petition anytime after the department refused to allow you join service as per directions of CAT.