What are the differences between 1600 & 140-series numbers, which TRAI said can't be blocked?

TRAI has said that calls from 1600 and 140-series numbers cannot be tagged or filtered by caller ID apps, adding that 1600-series numbers cannot even be blocked. The 1600-series numbers are used by government entities for government-to-citizen communication or by banks and financial institutions for service and transactional calls. Meanwhile, 140-series numbers are used for promotional calls.