Why can't the mobile phone receive short messages and the line is often busy?

This situation should be tested by substitution method. Let's use another mobile phone to see if it works properly. The problem of the mobile phone card can only be determined after the fault of the mobile phone is eliminated. If it's a mobile phone card problem, you can go to the business hall to get a replacement card.

The possibility of being cloned is very small, but it is not impossible.