My Mum recently changed her monthly contract. They sent out a new sim even though it wasn't needed and the old sim stopped working. After putting in the new sim her data is suddenly disappearing, a lot faster than it did with the old sim. A few other family members changed from the same, old contract to the same new one and have not needed a new sim. We don't know what is using up all the data.
Thank you so much for your first post to our community forums and welcome on board, it's great to have you on the team.
I'm so sorry to hear this has happened with your Mum's phone, it does seem odd that the data would be draining so suddenly. Can I ask if you have been able to check the data usage in the settings of the phone? You can usually see which apps etc are using the most data.