3 year old account

My gym account recently went into arrears and i have been in contact with the company trying to resolve it,i requested banking details and the amount to be emailed to me at the end of march, as i was in a serious accident in feb which put me out for a long time that expected, so accounts did get mishandled. so today i call to get the amount, only to find out from the lady that there's 2 accounts in arrears. I was absolutely shocked, she says there's an arrears amount from an account from JUNE 2013!!! I enquired as to why i was never informed of this amount before, the response is we never told people until 2015 about old books. I am absolutely livid as to why the account was never mentioned to me in a 3 year time frame. I would like to know why was my account was allowed to be transferred to the one using vitality with an amount outstanding and how do they expect me remember details on a 3 year old account. They have never notified me and always only informed me of current arrears nothing more.