[LA] TX apartment "rewrote" charges in a collection

The long and short of it -- I rented an apartment a couple of years ago in Dallas, TX. Two months into the lease, I could not afford it, so was facing eviction. I went to the property manager and made the deal that I would get out THAT NIGHT and eviction would not be filed. The unit in question was re-rented and had people in it less than two weeks later.

There's more drama to it -- ranging from the fact that the unit was unfinished and I suspect they tried to charge me "damages" for the unfinished features, to the fact that the property manager was very sleezy and did illegal stuff (threatening lock-outs, harassing non-stop voicemails, etc. etc.). He did this to everyone, and he's since been fired for being such a shit-show. (smug? -- anyway, it's brought up to explain why I think he would do the things I think have been done.)

Last year, several months after leaving the unit, I was contacted by a collector (surprise!). I asked for an itemized list of charges to be mailed to me, which they did. The list of charges totaled almost ~3,800 + interest. It included a couple of hundred dollars of "pet damages" (of which there were none) and over 950 dollars for an "illegal retainer fee." A lease break fee was listed, back rent, etc. All standard stuff for the rest.

I told them to pound sand on the pet fees and illegal retainer fee, because no eviction or court documents were EVER filed, and I challenge the damage fees.

We were flooded and I lost a lot of my belongings at this time, AND my job, so paying the debt was tabled.

Fast forward to present day.

I get a new call, from a new agency, that wants over $4,000. This would logically be the original debt plus interest. I tell them that I have no intention of paying the illegal retainer or the damages (but acknowledged I would work with them on everything else). At this point, the agency says there is no illegal retainer on the bill.

I ask for a new itemized list, because if they took off 950+ dollars, there's no way over $1000 of interest accumulated in just shy of a year. The math didn't work for me.

Turns out, they took out the things I challenged and then shifted the balance into other fees.

For instance, now they are charging me hundreds of dollars in "accellerated rent." This was never originally charged, and even if I owed it, I dont' understand how they can collect an entire years' lease worth of accelerated rent. There's no way I would have rented an apartment that worth double what I was paying. (I have asked for THEIR copy of the lease, which I highly suspect is now forged, and I am scrambling to find my copy -- the accelerated rent shocks me, as does the new '60 day notice' when I am certain my original was 30 days; I also doubt that the lease lets them charge a $1,600 lease break fee, because I would have run away screaming from this place.)

They are also now charging $1,600 for a lease break fee for not giving 60 days notice. (Mind you, I was paying ~890/mo. for rent.) The original itemized list was MUCH lower and FAR more normal.

tl;dr: Can they legally do this? Can they rewrite charges after an initial bill has been sent?

EXTRA QUESTIONS: I may have access to OTHER peoples' leases from the exact same time period. The leases would have been identical, save what was inside the "boxes." I know that their lease isn't my lease, but given that this is a complex that uses boilerplates, could it lend credence to my claim that the new lease is now forged?

IF I can uncover my original lease, and it is different than what is now being sent to me, what should my next steps be? Is this something I call someone over? What would be the dangers in pursuing this?