That is a real problem. But the same problem exists on many websites today, when you forget your password and have your eMail changed.

That is the reason, you should try not to change your eMail to often and when, keep the old adress until it gets cold.

Of course, what you normally should do: Change your eMail-address in the application before you switch.

AND: Never use your ISPs eMail-address (unless he will let you use it after you canceled your contract).