Songs purchased with an email that no longer exists

I need to know how I get around the following problem. Some years ago I purchased some songs and albums in iTunes when I had a certain ic24 email address. That email has not existed for some years. Today when setting up my new iPhone, it told me the items bought under that old email could not be authorised unless I entered the password for that account! Now there is no way that I can remember the password after all this time, but even if I did, the account and even the ISP ic24 has not existed for a long time anyway, so I had to skip over it when setting up my new iPhone. However, how do I get access to those old purchases now? And if I I was to try the 'forgot password' link, it would attempt to send a reset password link to an email that doesn't exist, so that can't work either. So how do I get authorisation for music I purchased long ago when I had a different email address? Thank you.