I have made a terrible mistake...need advice

I apologise for the formatting. Using my phone.

I escaped Retail 2 years ago and swore that it would be the last time I would work in shitty, shitty retail.

Cue 6 months ago when a job I loved decided to make 'budget cuts' and I was left unemployed. 5 weeks ago the 2IC at my old retail job said her store was looking for someone to do a specific job...I didn't want to do it but, begrugingly accepted it because I was sick of being stuck at home with no job and people kept telling me that "the job will be easy" (keep in mind, these people have never worked retail)

No.

I started 2 weeks ago and hated it 3 days in. I am unable to refuse extra hours and next week I have a 50 hour work week...that I apparently can't refuse. I just want to do my rostered 3 days a week!!.

I was told that I would be working out the back with another person as "one person can't do this job alone"...too bad they're not willing to train up the other person. The store managers reason? "Newbie has never worked retail and doesn't know what they're doing and I don't want to waste hours on them". When I offered to train the Newbie, my suggestion was immediately shut down.

I am lifting 100+ heavy boxes a day without any aid and have to be quick about it. I don't even get a flat top trolley to move them around with (apparently we 'aren't allowed' to have them as it's a hazard??).

I was told I'm free to take my breaks whenever I want as it doesn't affect any of the staff on the shop floor, only to be judged whenever I take lunch/10 min/toilet break.

The anxiety of having to deal with customers is creeping back up too.

The managers told me that the last person in this role took alot of sick leave and constantly cried injury. I can see why. They also judged the amount of times she went to the toilet: "Like, 5 times a day".

I had last week off because of prior commitments and was seriously considering emailing my resignation...but people keep talking me out of it because "money".

I'm truly grateful to my old boss for calling in some favours to get me hired and I don't want to burn that bridge but fuck me, this job sucks. I am a hard worker but already feel like I'm being taken advantage of by the store manager.

Should I stick it out until I get another job, or just leave and deal with being unemployed again?

I'm strongly considering the latter but would like to hear the opinon of more level headed people.