is saying "i'm sorry I didn't know you were confused" rude?

No. But your question is confusing to me. Sorry. What can I help you with?

Professionally, it's often better to be quite impersonal. Consider the difference between "There is a misunderstanding" and "You misunderstood." It would have been better to say "I didn't realize there was confusion" and left the "you" out of it.

Since most young people have rarely been on the receiving end of good customer service skills and most employers give little training in customer service skills, a great many young people (and even not so young people) who work with the public lack even basic skills like "Say please, thank you, and don't call the customers 'Sweetie'." So we customers must be alert and ready to provide prompts and cues like "I've been waiting a while; have I been forgotten?" Sigh.

i dont think so, theyre the ones being rude for ignoring you

squeal on them to the manager. write an email

If you feel you have been treated inefficiently, contact T-mobile's Head Office and share your observations about the treatment you received. All too often people in customer service do not pay attention and are sometimes indifferent/not interest in potential customers. It is unlikely you were not perceived as not being a customer given that - in theory - anyone walking through the door is a customer.