Many SMS issues are network-related. Contact your carrier for advice on possible network issues.
In rare circumstances, SMS messages can become stuck in a pending state and are unable to be sent. This can be resolved by a system update.
These are the typical paths:
Third-party messaging apps may also cause multiple duplicate SMS messages to be received. Clearing the data cache may resolve the issue. See How to wipe your cache partition.
A factory data reset can also resolve some software issues.