another option is to get a price quote for a replacement unit..then inform the landlord you are going to get it done and deduct it out of rent?
No, that is never the advice, and you should not do that.
If you can answer my questions about proof then you have something to move on with. If you don't and you haven't kept records or have relied purely on phonecalls which you haven't logged, then the time lapsed is largely irrelevant.
You should not be undertaking anything by way of gathering quotes etc yourself at this stage.
You could do with establishing what form the contract exists between agent and landlord - ie. has the agent been given delegated powers to deal with repairs on behalf of landlord, or does obligation in first instance remain with the landlord?
As per usual, written records are always better than phonecalls...