Finding the balance between giving and receiving is difficult.
And more so for individuals, like yourself, who are called to being of service!
There is an article, "pitfalls on the way to becoming a healer", that you may find useful. Search it at SpiritLibrary.com -- it is of a spiritual nature/source, which isn't for everyone. (There are also others about healers needing to be self-loving and self-nurturing, but I don't know the titles offhand.)
For your parents. It sounds as if you are doing more than what you reasonably can or ought to be expected of you. Unfortunately, this is also part of what is keeping them stuck in the problem of their own creation and lack of learning any better money management skills. It is you enabling them.
If you wish, you can help them with the solution -- but it's not your responsibility: Find out what credit counseling services are available in their community, and give them the list. Sometimes there are workshops at libraries, service clubs, faith-based organizations, etc. You could also check on-line if there are any household budget articles, templates, etc. I don't know what the banks are doing now, but in the "olden days" they were also a resource for this type of thing.
When you give them the list, explain pretty much how you've done here. Tell them you love them enough to "teach them how to fish", but it is their free will choice whether they're going to learn to fish or not.
Regardless, you also love yourself enough to not take responsibility for the consequences of others' choices, you've also been finding it financially difficult, and are unable to contribute to their household any longer. It is absolutely no reflection on how much you love them and appreciate all that they've done for you and what they've had to endure.
I know it's way easy to type, and a lot harder to actually do.
Sending hugs, and best wishes to all of you -- and good luck with your studies and career