Mail using 50GB of storage?!

Can anyone please help me with this. ‘Mail’ is using over 50GB of storage on my iPhone X. I have been to the apple store, they reset my phone to factory settings which seemed to solve the problem. The day later, the storage started creeping up again. I have reset numerous times myself which results in losing all my apps and some data. I have deleted the ‘mail’ app and started using the outlook app instead but doesn’t help. I have removed all email accounts from the phone and re-entered but it doesn’t stop it. I’m out of ideas and losing the will!! Any help would be great! Thanks.