بسم الله الرحمن الرحيم
There is no harm in learning and teaching of CA course as per the mathematics but it is not lawful to audit the interest based accounts. However, it is lawful to audit the accounts of lawful business correctly. It is not lawful to audit fake calculations and give fake certification. There is no harm in learning the mathematics no matter if it contains interest based subjects. Also, there is no harm in teaching it.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.