Stevens 555 firing issues

Hello all,

I have read post from owners of the 555 with issues of both barrels firing at the same time. I own a Stevens 555 in 20 gauge and the gun worked great.
Last week, I purchased the 555 in a 12 gauge and went out to the skeet range to try out my new purchase. First shot, both barrels fired.. Not a "Boom - Boom" but one loud BOOM... I reloaded and tried a second shot and the same thing.. I switched from m the "over" barrel firing to the "under" barrel and the problem stopped..

I will be contacting Savage and not accept a new gun that is not 100%.

If anyone has experience with dealing with this issue and Savage Customer Service, I would appreciate any advice.