The problem is that the second sentence is incorrect. In the simple past tense it should sound like: Your teaching request was successfully submitted the difference between this sentence and the first one that you've written is that if you use past simple tense it means that the action is over and that it was over for some time eg. it WAS submitted. If you say it HAS BEEN submitted it means that the action is over just before the moment of speaking, it has happened immediately after you've said it, while the past tense suggests that the action was long over. However, the construction that you've used, WAS BEEN does not exist. You could say 'Your teaching request was being successfully submitted', and that means that while something else happened in a distinct point in time, the submitting was happening, it has lasted before some action and had continued after that same action. I hope I've menaged to clear something out!

Simple answer: "has been submitted" describes the present situation (ie. the institution now has your request). In comparison, "was submitted" describes only the past, and tells us nothing about the present... in fact, we can safely assume that the past situation is different from the present situation.