What can possibly happen to my line for it to went off totally as if the line is not inserted

Hi Sulyman, it is likely that the SIM has gotten damaged, try and insert the SIM in another phone possibly a small phone, if the issue persist, you will need to do SIM swap.

To swap your MTN line,
Visit any MTN service centers or connect stores nearest to you with the following:
Phone Number,
NIN Slip or Virtual NIN
Your full name, date of birth, state of origin and mother’s maiden name.
4 Regularly dialed numbers within 30 days.
Last recharge date and last recharge amount
SIM Pack or Damaged SIM with Serial (for damage SIM only), or other evidence of direct purchase/ownership of the SIM
Cost is N400 but you might be required to also buy airtime.

You can dial *123*7*1# to get information on the location of any MTN shop closer to you.
When you dial the code, you will be required to enter your State, then your Local Government Area, you will receive SMS on the nearest MTN office address in your location, or you can use this link: https://www.mtnonline.com/personal/find-a-store/