Why don't China Mobile send short messages after its mobile phone recharge is successful sometimes, and sometimes it takes a long time to send them?

Excuse me, do you pay in the business hall or recharge with a recharge card? If you are in the business hall, do you owe money? If you owe money, you won't send a text message to remind you. Besides, please see if it is the end of the month or the beginning of the month. When the mobile system is busiest, there will be a problem of short message lag. Isn't there publicity at the beginning and end of the month to avoid paying money?