Text Messages not arriving after a few Days

When sending a text message, first, the message is transferred from the sender phone to the provider of the receiver. The provider then tries to transfer the text message to the receiver phone.

If the first try fails (for example because the receiver phone is switched off), the sending is tried again and again in regular time intervals.

Depending on the mobile phone service provider, text messages are usually deleted after 2 till 3 days or a maximum of one week. After that time it is no longer tried to deliver the message anymore.

Of course, you have to ask your provider how many days he will keep the text messages, because I do not know what provider your mother has, but I think that this is the reason why the text messages are not coming through.

In future, I would rather call your mother than sending additional texts, unless she keeps her phone on or controls it regularly.
2016-10-23 at 14:28

One more tip from me: it is possible to set up a delivery confirmation or notification in the settings of your mobile phone. Then you will be notified whether the text message could be delivered or not.

Additionally, there is a setting called something like "storage time for text messages". You can try to set this setting to its maximum, but I cannot tell you whether the mobile phone providers are caring about this specification.
2016-10-25 at 23:08