Added Amount on Invoice

I was due to move into a 2 bedroom flat @The Junction on the 1st of September, but due to an emergency, moved in the 25th of August into a 1 bedroom. To my surprise today I receive an invoice that I owe a month's rent, I am in shock because as far as I know, I paid all my fees and nothing is owed. I was told that moving into the 1 bedroom, nothing changes, there was a promo running for a month's rent free when I was approved for the flat, no one told me that, that did not apply now that I was moving to the one bedroom. There is no written correspondence. I have a list of emails going back and forth with the 2 agents - Jonathan and Tumi , where I keep asking if everything is still in order and the same and no one cared to tell me that things have changed. I am shocked and appalled that only today, after I have been there for weeks, now stories are coming out that I owe money which I don't. It is wrong and unfair, and I cannot be expected to pay this money. Whether they are trying to cover their backs in the Centurion Office or what, since the admin lady in their MIdrand Office was not aware of any promotions or whatever is happening - I do not know and do not understand.

If I was really supposed to pay rent, I would have been informed in writing, everything changed on paper, nothing was, only my lease was added with hand written notes after I signed it, that I owe money.

I do not understand how they can do this to tenants and pray that they resolve this, because I do not have this money and I cannot pay monies I don't know.