Why does my telecom mobile phone have a "national SMS information fee" from 4 yuan every month for several months from April this year?

It may be the kind of "information fee" generated by subscribing to the services of some telecom operators. If you don't cancel your subscription, you will be charged monthly.

Call 10000 to confirm. Since you didn't send this message yourself, your money will be deducted every month. Maybe the service provider behind forced you to open a charging service. In this case, you can directly ask 10000 to refund the fees deducted in the past few months, and you should protect your rights and interests yourself.