Job advice and help please

I'm 26M working as an assistant restaurant manager. I am currently getting £1630 a month with accommodation and food. I graduated last year with a masters degree in hospitality and tourism management from a good university in the UK. I didn't choose the post study work visa for 2years and opted for the skilled visa with these guys as it would count to getting my permanent residence in the UK. I am currently on a skill based visa here which is why my salary is low and the owners won't be increasing it during the 3 years I have to work w them it's already been 2years tho. We don't get any tips or service charge as the owners take them, I am currently working around 55 hours a week with each day working from 11:30-10:30pm straight shift (but I take a break as and when it's not busy but still have to be at work) but for December I have to work 6 days which is around 60+ hours. My contract is for 40 hrs a week but can't do anything about it. The people I work with are not educated enough so I have to deal with all the problems occurring in the restaurant as the others can't speak English or can't work technology etc even it if is not my job. The owners keep asking me to do things which are not part of my job like doing social media,marketing,photography along with all the operations of the restaurant and dealing with vendors and staff as well. The owner has also opened a takeaway place with a dark kitchen for catering which is a huge kitchen and is not picking up which causing a loss. They open things without doing any research whatsoever and expect it to work. We don't get paid on time either as they say they don't have money right now (he drives the latest Bentley bentayga and the new range rover 💀) Sometimes I don't get paid for 2-3 months so do the other staff which leads everyone to be depressed and angry as everyone has bills and needs money for family etc. They pay £8 hr for front staff which is why I have hire people who are either not fluent in English or want cash in hand jobs but then the owners crib about the service not being top notch? Like dude if you're paying less than minimum wage I can't get exceptional staff... I don't know what to do, I am tied with them till January unless I renew my contract with them for another 2 years which idk if I'll be able to do. They will show an increase in salary on paper to the HMRC but I will have to refund them the money in cash as the other guys who have renewed their contracts last month are doing. I am a sharp and well educated guy and I feel I am wasting my life doing this job,I have started drinking a lot more because of this and Idk being at work the whole day doesn't really let me do anything else in my spare time as I am too tired to do anything when I get around 11ish change and then it's midnight already. I need to find another sponsor who can hire me but my family thinks I should just firm it and keep doing this which I don't want to do. I was thinking of starting to study for cemap qualification on the side but I don't know if that's a good option, if anyone reading this has any knowledge please let me know. If anyone has any other suggestions please guide me I am losing it working with these people