Yes, you do in fact need multiple tests to confirm a diagnosis. Any diagnosis, let alone cancer.
EKGs and echocardiograms (ECGs) are the same thing. ECGs don't diagnose lung cancer, but my guess is that you're an average american and thus have some kind of heart problem, too. An ECG is a visual representation of what your heart is doing typically over a 3-6s period.
Lastly, you are not a "consumer" at a hospital. You're a patient. The distinction is important, for basically the exact reason you describe as frustrating. The only way to bump yourself up the priority ladder is to be closer to death. There's no manager you can try to harangue into giving you "better" treatment. You get the level of care that you need. If you legitimately don't receive at least that, then yeah, be upset.