Are there any free plugins/extensions which send the OTP through registered email as well as a mobile number during the registration process?
I haven't personally investigated or tested any of the following, but a quick Google search for
Joomla OTP verification revealed:
You should take it upon yourself to download and trial these extensions so that you can come to your own conclusion about which one is best suited to your application. Please always do your due diligence before asking for help/support/advice.