Insert sim problem can arise under different circumstances may be they have been rejected by your cellular provider or there has been some hardware issues.
Things you can try are :
First and foremost ,connect with the cellular operator and just check whether any issues with sim card registration,as there are chance that they might have blocked your number.
Secondly,you can do some cleaning up your sim card slots,maybe that solve the issue.
There is a final solution ,i.e jumper solutions (resetting pins in your phone circuit),It is recommended to proceed with jumper reset if you are aware of circuit behaviors ,else consult your authorized dealer for the same.
ramakrishnan