Thank you Beth. I tried this several times on Saturday but went round and round in circles. They wouldn't verify me because I couldn't tell them the name of the original account, company registration number or where it was registered. They then said they would close my mailbox in 30 days time completely. I have no way of getting this information and have been using this email address for many many years as an individual. It is causing me great distress. Is it worth trying them again - is there a way I can escalate it?
