First you should check that the number you have provided in the  website is correct or not. If correct then you should try to verify your number someother time. Now if didn't happen at a later time also then I would recommend you to switch the sim from the phone you are using to another phone and try to verify it. Sometimes this problems occurs due to the phone message memory space if you are using old mobile phones. So it will be better if you try some later time and then also if you don't receive the OTP then I would obviously recommend you to switch the sim to any other phone and then try to verify.

To know more about NEET visit the link below:

https://medicine.careers360.com/exams/neet

I hope this answer helps. All the very best for your future endeavors!