Record all calls.Speak each time that the person called at time/date, and why is he calling ........... times each day, What is his name/designation/name of employer (agency)/address/Manager of M/s Axis bank in charge of agency etc?
Ask him to stop making phone calls at once, if you do not want phone calls.
Maintain call log: date/time/day
Send call recordings/call log date to local BM, MD, Chairman of M/s HDFC Bank ( email@example.com) , RBI (CPED) and post your demand...................
Whatever be the reason, you are expected to pay on time.
The recovery/collection agents can not harass and litter nuisance.
Lodge complaint with RBI as well.
You can download the details from many threads e.g.: