To help prevent fraud if your cell/mobile phone is ever stolen, make sure that your SIM card is locked.
Because phone security is very good these days and prevents robbers from being able to access your phone, it is easier for the robber to simply remove the SIM card and put it in their phone. This will then give the robber access to any OTPs or phone calls that would have been meant for you.

Your SIM card will come with a PIN (Personal Identification Number) which you can use to lock and unlock the SIM card. If you have to turn off your phone or restart it for any reason, you’ll be asked to the PIN in order to unlock the SIM card.
What this means is that if your SIM card is ever transferred to a robber, then they will need to know the SIM PIN to unlock the SIM.
That means that your SIM cannot receive OTPs or any phone calls.
The way to lock or unlock your SIM is done in the phone’s SIM manager settings.
If you don’t know your SIM’s PIN, then look at the information that was delivered with your SIM card.
If you don’t know the PIN then you will have three chances to guess the PIN before your be asked for the PUK code.
Look on the card that your SIM was installed in and you should see the PUK code. If you don’t have that card then log into your cell/mobile phone account and you you’ll be able to see the PUK code there.
If you still can’t see the PUK code then you will need to call your cell/mobile phone provider and they’ll be able to give it to you.
DO NOT try to lock your SIM unless you have the PUK code otherwise your SIM will be permanently locked and you’ll need to replace it.
Many phones now come with eSIM capability (embedded SIM) and offers additional functionality like being able to add multiple cell phone providers to your phone in additon to preventing your SIM from be removed. If your phone has an eSIM on board then I suggest that you convert the physical SIM to an eSIM. Your cell phone provider may charge a small monthly fee to but it is worth the cost for the enhanced security that an eSIM provides.