I have used Elixir strings for about 3 years now. Never had problems with them..
Do you have a flying bridge, such as a tremolo, floyd rose bridge?
When you start releasing the tension on the bridge due to the other strings, the bridge comes down, if you forget to downtune the others then the tension on those strings will become so great that they snap.
If you have a locking nut, beware to unbolt the nut before tuning your strings. They will also snap.

And, next time. Keep the reciept, and take the broken strings with you to the store.
You can always buy Ernie Ball Slinkies, they can stretch really far without breaking. However, they will not last as long as Elixir's Anti-Rust strings.