What should I do if I cannot provide the required tax documents for my mother's dependent visa application in Thailand?

I want to apply for dependent visa for my mother as I am working here as a teacher. When I applied for the same at the Immigration ,the officer asked me for the detailed tax papers, as whatever Tax papers I had was not enough for the application... Now the problem is ,the school cannot provide me the detailed one... Not enough time for applying as Coming Monday is the last day for application .