Assalamu Alaikum Warahmatullahi Wabarakatuhu,
I would like to know,
if i'm not sure if a certain food is contaminated with any other haraam food, contacting the people who owns the shop without my parents knowing. Is this wrong?
Talking with people is, in itself, not haram if the subject is not haram.
The only way I can see this as unlawful is if your parents explicitly forbade you from calling the shop, or using the phone, or another such order that conflicts with you calling the shop.
However, the fact that you are specifying "without my parents knowing" seems to indicate that they would disapprove of this. And if you know this to be true, if you know that, if they knew, they would disapprove, then I would advice against it.
I don't know how old you are, but parents often have good reasons to keep children from talking to strangers.
You should probably have a discussion with your parents on the subject.