Why can't mobile group texting be cancelled?

The system is busy and the contract is limited.

1. The system is busy: when the system is busy, it will be unable to cancel the group SMS, and the operation will be cancelled when the system is idle.

2. Contract restrictions: there is a contract in the package, and the contract period is long. Public SMS cannot be cancelled during the contract period, but it can be cancelled at the end of the contract.