How to shrink a loose silicone material phone case?

Ok so i have an iphone 4 and my first silicone phone case became loose within a month and i ordered a second one but after a while the same thing happened. Rather than buying a third one i've heard there are ways of shrinking silicone phone cases but i'm not sure how if that is true. If you have any suggestions or tips please let me know.

Put it in hot water then on your phone so it molds

I've gone for a TPU case now, it's flexible but harder than silicone so it doesn't go baggy. I paid about same price as a silicone one.

Putting the case in the freezer for a couple hours. I doubt this would be a permanant solution though due to it warming right back up. Heating it up would just make it more flexable and looser.

or would this issue be good for warranty? You can try it.