I feel for you so much right now @CheerBear. I'm glad you were able to put into words how this whole thing is affecting you and hope it helps you take a small step back from it all and observe what's going on and break it down. None of it is your fault. This system seems designed to break people at times, the very people it's meant to help.
Not sure if I've told you before but if you have a plan manager you can also use service providers that aren't NDIS registered (in my case that's the psychologist weekly). If you had a plan manager so much of what's getting on top of you could be taken care of by them. I'm just wondering if it would be a good idea to get one - talk to NDIS about how to do so but I think it involves requesting a review of your plan so you can get plan management included.
Great idea about getting a support person (informal i.e. friend or family member) to come to meetings with you. That was a great help for me. If no-one is able to do it you could request an advocate through Disability Advocates which are free and in every state (google them for where you are). I had one and they were a huge help and also came to meetings with me (as did my sil and sometimes my bro as well). It really p's me off that a lot of people with 'psychosocial' disability (MH challenges) are exactly the people who are unable to advocate for themselves, especially when over-whelmed by the intricacies of NDIS, and frequently isolated in a way that means there is no-one to support and advocate for them.
Did you have PIR or someone help you when you were applying? Maybe a good talk with them would be helpful too.
Re funding for housework etc - I have it too and don't use it. I think it's in there because of some of the details of the functional effects of my disability - we presented what I'm like when my worst days happen, not what I can do when at my best. But as it's in core funding it can be transferred to another category within core funding and used for e.g. community involvement or enhanced health and well-being.
Do you have psychology funded? I think they won't fund a mental health worker as well as they likely deem it to be a service available through 'mainstream and allied' mental health (public health or medicare rebatable). Maybe. What do you want that person to be doing with you? There may be another way they could claim from your plan e.g. improved relationships, behaviour management or something like that. I specified to my CoS that I wanted SWs who were mental health trained, not just peers with lived experience. And she found them. And they are helping work out and implement strategies to work towards my goals.
I'm just throwing ideas around here in the hope something is possible out of all I've suggested. Again, I'm feeling it all with you and hoping you are managing otherwise, family needs etc. Take good care xx