For Tan No.

While applying for new Tan No. , too many problems arise from the last 4-5 days....... First of all, the portal shows Site under Maintenance , after taking too much time it comes ..... but then the problem comes for A.O. code,  usually I used as per my city's A.O.code & ward till date, so I type there the same no. because it isn't in the list of what portals have. So what should i do now ?? shall i use neighbour cities A.O. code which shows in the list ?