Start here — why the usage is higher than the headcount
The audience was 5,741 people, but the account was billed 11,482 messages.
The message runs to 276 characters. Carriers bill SMS in segments of roughly 160 characters, so a message this length is sent and billed as two messages per recipient, not one. That, rather than a second campaign or a repeating send, is what put the account over its SMS allowance.
Bringing a future message under 160 characters would halve the billed volume for the same audience.
5,741 recipients× 2 segments= 11,482 billed messages