Welcome to the forum! You made a great decision by choosing Audi.
First of all, look under the steering wheel, there is a small column and there should be a black cover with the manual inside. Don't worry, a lot of people have complained about the missing manuals
Now to your problem: I believe, from your description, that you or somebody else have manually, involuntarily set the "speed limiter" to that speed. You can turn it off using the buttons on the "edge" of either the turn signal lever or the wipers lever. Pardon my bad English. I don't exactly know how to turn it off but it should be in your manual

Is it auto or 6spd? Mileage/price?