"Insubordination"

Using a throwaway because i know my manager uses reddit.

Ive been working for petco for about 2 and a half years. Im the animal operations specialist, and the store is small, yet very busy. We have very few staff yet little to no hours. My store manager (whos worked here for 10 years) is a pain, (as well as our DGM but ill get to that in a moment) and i am incapable of communicating anything to them. I have autism spectrum disorder, and my managers are aware of this. I need open, clear communication, and i struggle to work against a schedule. I specialize in aquatics, and while i try to spend most of my work day in aquatics doing maintenence, my manager makes it so the schedule sticks me up at register for the entire day. Every day. For 5 days a week. I open the store, and unless i am misremembering, stores are required to, when opening, have:

1 manager 1 animal operations specialist 1 solutions generalist/cashier

When opening, its just me and a manager. We are far too busy and high traffic to accomodate that, and it becomes stressful because we then dont get any cashier until 1pm. I then cannot clean the tanks or clean bettas because i get stuck up front for 7 and a half hours. None of the staff clean the tanks other than me, even though i have asked on multiple occasions for help, and its increasingly frustrating. My manager constantly complains how the tanks are dirty and when i try to explain that i am unable to do it when i am trying to manage registers, BOPUS, truck and animal opening, they ask me in this condecending tone "are you being insubordinate?" Or "are you questioning my authority?"

My manager has made multiple comments about my intelligence to my face (such as "use your brain for once"), and their distressing behaviour has become increasingly difficult to handle. I am struggling mentally, and i fear for my job because i require the insurance for my medication. I often think about going on LOA because i am close to a mental breakdown, because i have no energy or will to do anything else anymore. I am trying my best and doing 500% of what i can do, yet no one else is willing to put in the effort or has the work ethic to do so and im stuck being shoved around. Our DGM doesnt make it any better because when i attempt to bring up any issues with them, or try to ask questions, they say the same things my manager says: "are you questioning my authority?". The other leaders say im not doing anything wrong, and that im not being insubordinate, but i feel like i cant even communicate with my manager without it becoming an "attack". What do i do? HR doesnt care, and im on my last strings with this company. I love working with animals, but i cant do my job if im not in my department. Any advice?

Edit: i also feel like i should clarify these two things:

1: i know the definition of insubordination. I dont think im being insubordinate 2: I become distressed when things are moved around or changed without my prior knowledge. This is a huge communication thing for me, as i am very adimant about plano. My manager does this often, moving plants around for example, and i cant do anything about it because if i ask for them to at least tell me theyre doing it, i get told im being "insubordinate"