Call 4445 with your mum present and they will let her know whats happened.
if on PAYG she will be on a Big Bundle which probably isn't the right tariff for her if your Mum just uses her phone for texts and calls https://www.o2.co.uk/help/pay-as-you-go/big-bundles
Mum may be better off with a Classic tariff where she just pays for what she uses.
Available on Tesco and Giffgaff (on the O2 network.)
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