I tend to avoid vendors who don't have good customer service (within reason) simply because there are some excellent vendors out there who make fantastic stuff, and who do respond to emails. I don't think toasting your juice in your glove compartment is going to eliminate the mint (and I have never had key lime pie that had a mint flavor, even slightly) but that sounds like a "quick" steep method, so you may find it mutes the mint enough and blends it in with other flavors, enough to be tolerable-- but the company is basically telling you they send out presteeped juices, at least sometimes, if that was their remedy. I'd try it (no harm if you hate it as is) but if you do that and still hate it, I'd be asking for a refund (unless mint was part of the description.) I find it unlikely that steeping that way will eliminate the flavor, but it may blend everything more....
I'd say try another vendor and some different juices, follow Broke Dick's method and see if it changes anything, if not request refund or obtain one via your payment method (bank, paypal, etc.) Did they say for how long? Don't wait forever, in case you wind up needing a refund....
Anna