No, with your current qualifications (12th PCM and BA), you wouldn't be eligible to join the Officers Training Academy (OTA).

OTA requires a candidate to have a Bachelor's Degree from a recognized university in any discipline.

While you mentioned not having studied Math for a long time, there is no specific requirement for appearing in the OTA entrance exam (Combined Defence Services Examination - CDS) to have Mathematics at the 12th or graduation level. The CDS exam syllabus focuses on:

• English
• General Knowledge
• Science (Physics, Chemistry, Biology)
• History, Geography, Polity (for some posts)
  
  I hope it helps!