Firstly I would like to say you are not a failure - f**k your school, you got a degree so you have already proved them wrong. You motivated yourself to do that in spite of the bullying and in spite of being told your a failure - and not everyone can do that.
I also really feel for you, it sounds like you are going through an incredibly rough time. I'm not sure if any of this will help but I'm going to list a few things which you may or may not find useful. You may well already be aware of them.
and see if they can give you any advise on managing your debt. I suspect you've already cut back a lot but I'm also going to throw this one in here https://cookingonabootstrap.com/
- a whole website of cheap recipes that may or may not be useful.
It also really sounds like you need some face to face support so if you can try and get an appointment to a GP - tell them you are struggling, tell them about the grief - they may be able to refer you to someone to talk to. I suspect your Mum would probably like to help you too even if she does have a lot going on her life right now and she might also need someone to talk to if she is also grieving? I can only speak from my own experiences but I know talking can help me work out my problems myself simply by saying them out loud to another person, but everything is different for different people.
Take every day one step at a time. Life can be incredibly overwhelming at times so I'll pass on the advise my counsellor gave me once. Pick just three things you want to achieve that day. They can be something as simple as doing the washing up. At the end of the day if you have done them you have succeeded. Start small until you have enough energy to do more.
If you're awake at night worrying about things you need to do. Take a piece of paper write them down ready for the morning and try to sleep - sometimes this helps me because it then feels like I have a plan.
I hope you get the help you need to make it through this. You have already survived so much keep going.