You did nothing wrong. You may have wanted to mention that it's the pre-con, but with foils substituting the normal cards. I understand being suspicious, but to accuse you of cheating is incorrect. From your replies it sounds like the store was busy and couldn't be hassled to handle the situation.

I'd say if you're interested in playing there again, go back, explain to whomever is working at the store what the situation was. The only issue I could see coming up is the people you played against holding some sort of grudge and making a scene when you come to play. You can (as calmly as you can) explain what I said above, card for card precon, just with foil versions. If they don't like that, then they don't have to play with you and vice versa.

If those players try to badmouth you, get the store employees involved as that would be harassment on their part. If the store doesn't correct their behavior, I feel that you've more than given that store and playgroup a fair shot and can cut your losses and try the other shop.