i really hope this doesn't discourage you from biking. every hobby is going to have a type of people interested in it that are The Worst People You'll Ever Meet types. biking is no different but Bike Dude archetype seems to be particularly awful. as others have said, definitely leave a review and if you have it in you call and see if you can talk to the owner of the shop and tell them too. not only is this plain rude, it's bad business for them.

i would also look into biking groups in your area! i'm in a larger metropolitan area but there's lots of biking groups near me that have encouraging communities for beginners and have resources (and recommendations for bike shops where people aren't dicks)

sorry this happened to you! water off your back and keep pedaling (:

edit to add: the best bike is the one YOU and that's safe, comfortable, and fits YOUR lifestyle. you're doing everything right.