I'm sorry you were lied to but unfortunately this happens more often as not. Employees will tell you anything as long as you buy something. Like there is no animal or product that will keep your tank clean. Fish excrete ammonia and this is toxic for them. A nitrifying bacteria culture needs to be established first and foremost so they can be safe. Live plants will help, but as they often don't sell the right plants used filter media or substrate is better. With the test kits can be determined when the tank is cycled and when it is safe for fish. Right now it is not. Do a 25% waterchange when you get home. The best would be to get like a cup of filter media or gravel from an established tank and put that in your tank. Ask questions here, there are many helpful folks here to answer them.
There are probably other issues as well besides the neon/angel incompatibility (neons need to be in schools 8+) just like the catfish, which may or may not grow larger as your tank.