Just Letting Bloomingdales - Complaint - All for the Landlord

We currently has to vacate a property that we were renting. All locks and doors were working and I feel the house was returned in the proper state. We dd the exit interview in the 26.03.2020. Whilest we were in residence we changed the front door lock at our own cost as the lock jammed. Now on exiting the property the landlord wants the lock replaced as apparently it is a specialised lock. Now where in my contract nor the ingoing inspection was this mentioned. Now the landlord wants the working lock replaced with another specialised lock whic I do not agree with as we had no knowledge of the lock being specialised to begin with. Just Letting PE, Bloomingdales has no ones interest at heart other than the landlord. They are not witholding R1200 for lock replacement with a lock smith which any handy man could replace and I also feel that I should not be paying for this as the current lock works perfectly. They threw the contract in my face saying that the contract says no alterations without concent but this was maintenance and we cant take time off work for maintenance people to come all the time for a simple lock. Then the consultant does not want to give me her managers number or email address for me to make a complaint. I am so disgusted as I pay the rent and never defaulted and am a tennant that does complain alot.