Sewage Volcano In My New Apartment On Move In Day, Need Help!

Howdy guys, I've got a real conundrum here as I try to move into my next apartment. I had signed a lease a few weeks back and submitted it to the leasing agent I previously had contact with, we'll call her Contact A. Contact A did not disclose that the property was picked up by another leasing company around the time I had submitted that documentation. It was only until yesterday (Thursday) that the new company had reached out to inform me of a newly updated cashier's check, etc. This is how I was introduced to Contact B with a slew of new information out of nowhere. Already off to a shaky start as I was left in the dark on that until less than 24 hours before my original key pickup time at 10 AM today (Friday).

I got everything taken care of and went to my morning meeting at the new leasing company's office, where I met Contact B. Contact B thanked me for my due diligence in sending the requested info over (renter's insurance, etc.) in a timely manner. I handed her the cashier's check, she gave me the keys, and me and my girlfriend were off to check out the new place! This new unit is only under my name.

~30 minutes later, we arrive on site and enter the apartment. The smell was overwhelming, dude. Immediate stench of a septic tank, which is basically what this apartment became. Water, piss, feces EVERYWHERE. The toilet looked like it blasted caustic butt-spuds everywhere that turned into oatmeal on impact with the floor. There was probably a solid 1-centimeter worth of water spanning from the whole bathroom down the unit's hallway along the edges of the living room and nearly to the kitchen. The bathroom is right next to the bedroom, which is carpeted. We have photos that would suggest the carpet was affected by this, but we could not get close enough without wading through the diarrhea swamp, which we opted out of.

I called Contact B to inform her of what happened, she said they'd get emergency maintenance out right now. My girlfriend insisted we head back in person, and I'm glad we did. My "project manager" greeted us instead of her, introducing himself as Contact C. He said cleaners and plumbers were heading there as we speak and would update me later in the day. At this point, it has probably still been less than an hour since key pickup. I intended to start moving boxes in today to save my big furniture for Saturday, when I have time off and a Uhaul reserved. I made this clear that I need that Saturday. By the end of the day, he called me to let me know that there was a main sewer line that backed up and hit my new (half?) garden level unit first. I asked if this was frequent in the past, to which he said he was unsure. He stated that the property was only obtained a few weeks ago and they have no records of ANY issues, from what it seems.

He assured me that after the cleaning, the plumbers, and the deep clean tomorrow (Saturday) that my new unit would be ready by 11 AM when I intended to start moving in. He also assured the sewage issue should not resurface. Now, I am going to be there in less than 12 hours. I have yet to see if it's clean, if it smells, and if it's livable. I am not only nervous that it will not meet basic standards as this company's reviews are a mixed bag, but I do not feel confident in living in a place that this went unnoticed for an unknown amount of time, plus no prior knowledge of building issues.

They have my money (a substantial chunk that I need to go towards my next place of living's move-in costs) and my name is on a lease that was done with the previous landlord/leasing agent company. My girlfriend and friends have said I should try to leverage cheaper rent, a new unit in the same building, a new unit at a different property, or asking for a full refund and trying to find somewhere else. Whether deemed legal advice or not, this seemed like the place to go to get opinions and I appreciate any feedback from you all, cheers!