I don't think that 48 ever sent texts for missed calls.
Most phones show a local notification for missed calls.
Perhaps enabling/configuring voicemail is what you want here?
But again I don't think that it involves texts being sent for missed calls.
https://community.48.ie/t5/The-Knowledgebase/How-do-I-use-my-Voicemail/ta-p/244
Hope this helps.
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