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Have you tried a soft reboot by turning the phone Off and On.
Remove the sim and wipe the chip carefully and re insert.
And if you can please try your sim card in another phone as a process of elimination to try and rule out the phone, sim card or account that might be at issue.
Perhaps try another sim card in your phone.
Is this happening in one place or elsewhere too @Stesween85
Current Phone > Samsung Note 9 _512Gb > Model: SM-N960 Hybrid-Duos.
Samsung One Ui / Pie.
Samsung Gear s3 Frontier Watch.