Just Letting has no regard for tenants- charging me for rentals after i have moved out

Signed a lease and stayed for 19months paying rent on time every month. After the initial 12months we got the renewal lease- only to find out that in the fine print, we could actually not give notice till the 12months were over. We then informed them that we needed an exit clause as we were actually looking to get our own place and they said we will then need to bring the proof of purchase. Around that time, we received summons at the flat in the owner 's name which we mentioned to them but got no follow up except that we should send the summons to them. We then got legal advise that if a sheriff was to show up which was highly likely as the owner wouldnt have seen the summons since they had come to the flat instead of where he stays. We then decided to leave sometime in April as our property was no longer safe and we knew we wouldnt get our deposit back as the place was in debt. They actually wouldnt sign release documents so the security wouldnt let us out. We eventually left wth some of our stuff and security woudnt let us back in so we could finish taking out our stuff and clean the place. Eventually i had a breakdown at the gate and they let me in but not for long so we cleaned normally. Now they send a bill for R22k incuding may rental, remotes charges, water bill which we were never told about in the whole time we stayed there. The Agent is rude, they send threatening mails and disregard our concerns. i never thought such a big name like Just Letting would underplay people like that. we work hard to be able to afford their rentals but cannot even be afforded a little respect in return. Now we being threatened with blacklisting and my whole life i have done without luxuries just so i can pay rent. Wish i never made contact in the first place. This has been a full on nightmare.