I was their customer for almost a year and I decided to cancel my account due to some reasons:
1. I found a cheaper web hosting
2. 1and1 customer service sucks. They keep you on hold for at least 30 minutes
3. They do not know how to handle customers.

Before transferring to my new web hosting, I cancelled my account about 3 weeks from my next billing cycle. I called their customer support and verified everything that if I cancel now, should I still be able to access my remaining weeks of my account until it expires. And the person said "yes".

But after confirming my cancellation, I wasn't able to access my account and the technical department told me that once you acknowlege your cancellation, your account is still active but I your account is locked. This means that you cannot access your files anymore.

I don't know what's their problem why they need to lock your account. You already have paid for it and there will be no harm if you cancel the account prior to renewal.

So, my advice is, before you cancel your account with 1and1, you have to make sure that you have deleted or backed up all your files prior to cancelling your account with them.

I DO NOT RECOMMEND 1AND1 TO ANYBODY.