@Michelle O'Connor You have reached Azure Storage Forum,
Please contact Hotmail community, this link will help you https://answers.microsoft.com/en-us/outlook_com/forum/all/hotmail-mailbox-suddenly-out-of-storage-after-25/8762ce65-ee59-470f-9616-76671152f474
Please do not forget to "Accept the answer” and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.