California Tenant Here. Landlord Is Charging Us Rent After We Moved Out And Didn’t Return Our Deposit On Time. Need Advice.

Hi everyone! I’m hoping to get some advice on a situation my husband and I are dealing with involving our former landlord. We’re in Southern California, specifically San Bernardino County.

We moved into our rental in October 2024. Our original lease ended September 30, 2025, and we signed an extension that apparently had an end date of October 31, 2026.

Here’s where things get confusing.

On August 28, 2026, our property management company notified us that our rent would be increasing starting October 1, 2026. Because of that, we were under the impression that our lease was ending September 30. We submitted our 30-day notice on September 1, and management accepted it without saying anything about us supposedly being responsible until October 31.

We had our final inspection on September 24 and returned our keys and garage remote by September 25. They even had the property listed as available for showings starting September 25.

Then, after we moved out, management suddenly brought up the October 31 date on our lease extension and said we were still responsible for October’s rent.

Our security deposit was $1,750. We expected to receive our deposit or at least an itemized statement within 21 days of moving out, which would have been October 16.

On October 20, they finally emailed us saying the owner had agreed to charge us only for October 1–15 instead of the entire month. They deducted $875 for rent and another $225 for other charges, leaving us with only $650.

We don’t understand how they can increase our rent effective October 1, accept our notice to vacate, take back possession of the property in September, and then turn around and say we’re responsible for rent in October.

There’s also another issue that really bothers me.
During our tenancy, we discovered that the property didn’t have any carbon monoxide detectors, even though it had natural gas. We have a toddler, so this is especially concerning to me. We genuinely thought the smoke detector in the hallway was also a carbon monoxide detector, but it turned out to be smoke-only.

When we brought this up to management, they actually admitted in writing that they had failed to provide carbon monoxide detectors. They had also conducted inspections during our tenancy, but somehow this was never addressed. We have emails and photos documenting everything.

At this point, I’m just frustrated and not sure what to do next.

I understand that we signed an extension showing October 31, 2026, but wouldn’t their decision to increase rent on October 1 and their acceptance of our move-out notice contradict that? Why wasn’t this brought up when we first submitted our notice?
I’m also wondering whether missing the 21-day deadline for our security deposit has any legal consequences, especially since they’re deducting rent that we’re disputing.

And regarding the missing carbon monoxide detectors, is that something we can actually take legal action over, or would it just be considered a code violation?

We’ve kept pretty much everything: emails, texts, lease agreements, inspection records, photos, and the rental listing.

Has anyone dealt with something similar in California? Would small claims court be worth pursuing, or should we speak with a tenant attorney first?
I’m not trying to get out of paying anything we legitimately owe. I just feel like management is contradicting itself, and we’re the ones paying for it.
Any advice would really be appreciated. Thank you!

Location: Southern California