Background
I moved into a studio apartment that had a $200 rent reduction, valid for 6 months through the end of December 2017. An employee with the property management company had told me to reach out before the period ended to see if we could extend the promotion period indefinitely, because they had done so for previous tenants.
In November, I reached out via email to formally request the promotion be extended, and if not, I would move out immediately in January. The property manager at the time replied via email, saying she would get back to me shortly. (Note that I'm not sure of her official title, but all communications with the management company was through this employee.)
After 2 weeks of no response, I emailed again. An unknown amount of time after that email, I called in and reached the property manager directly. She then said casually that yes, they already agreed to let me continue with the same rent.
Current situation
Fast-forward to April 2018, where I receive notices at my apartment door that management has changed, and the employee mentioned above no longer works with the company. Another notice is later posted, saying I owe backdated rent from January. I reached out via phone and leaving voicemails, and I also send emails to ask for clarification.
I also contacted the building manager who resides in the same building, and he had told me to not worry as other tenants were receiving the same notices.
Fast-forward again to May, when I finally receive a phone call from the new staff with the management company, saying I owe the backdated rent due. I forward my email correspondence with the previous employee, and today, I am told over phone that the lack of written documentation means I owe the backdated rent. She also indicates that other tenants have been getting the same notices and phone calls, so this situation is not unique to me.
I then give my 30-day notice over email, as requested, and I receive a call back from the same employee, saying the owner will continue honor my rent discount promotion from June onwards, but only if I pay the backdated rent.
Question
Do I actually owe this backdated rent?
It's suspicious that there were no notices for late rent payments until after new staff was brought in. Aren't verbal agreements binding?
(Jurisdiction is US, state of California.)