How can I unblock my mtn sim I believe it’s blocked because it’s been awhile have used it

My Mtn sim has been blocked and it’s asking for Puk number with the phone number +234 9137129360

I bought a registered sim card from an MTN agents at Ebonyi State,Ohaozara precisely,and it's was blocked recently,I have not been using it for calls all this while,what should...