If your MacBook Pro is still under an active Apple Care plan - any Apple store should give you a replacement without asking any questions - provided your adapter is not damaged from water or from obvious misuse. You can also call Apple Care directly and they will take care of the issue.
In the meantime - If you have another MacBook with a MagSafe adapater - you can use it to charge your MacBook pro - even if the other Mac's charger is not 85W. I am able to use the 65w MacBook Pro 13" charge as well as the 45w MacBook air charger on my MacBook pro 15" (which normally takes the 85W charger). The lower the wattage of the charger - the longer the charging will take. I believe they are 100% interchangeable.