Can HMRC change your National Insurance Number without informing you?

I am a international student and have been studying medicine in the UK for 5 years on a student visa. This March I applied for my National Insurance Number from HMRC which I have since received (in the form of official letter from HMRC). I have graduated and received an offer of employment from the NHS. I have used the National Insurance Number for my job application including certificate of sponsorship. I have converted my student visa to a Tier 2 visa and just received my Tier 2 Visa (Health and Social Care) from UKVI. I noticed my National Insurance Number in my visa was not correct and called UKVI who informed me to contact the Department of Works and Pension or HMRC as my National Insurance Number has been changed to the one they have. Is this possible? Please advise what I need to do to clarify the situation. As far as I am aware the National Insurance Number I recevied back in March was exclusive to me and cannot be changed.

Hi Dav Chng,
The National Insurance Number you were given should not have changed.
Can I suggest you contact the National Insurance helpline.
Lines are open 8am – 6pm Monday to Friday.
Thank you.