Owner deleted old lease from webportal saying we now owe $2550/month + backpay instead of $2450/month

Hi all, just moved to California 2 years ago and found this place that charged $2,300/mo. We went to renew our lease and they originally said $2550/mo but we negotiated down to $2,450. After we agreed we never got charged, asked management when the new lease amount would start and they said not to worry it would be next billing cycle. Well there was a change in management and radio silence...."magically" our lease was deleted and now temp managers are suddenly asking for $800 in backpay (even though it didn't start until September) and are saying we owe $2,550 for Dec rent tomorrow.

Normally we print and save the lease but with all the negotiating we didn't think to do it, let alone it sounds like it got deleted not longer after we signed it. The only evidence we have that we agreed to the $2,450/month are emails with the old manager saying ownership agreed to that newly negotiated amount.

What can I even do about this? We contacted the temp manager but they can't do anything, tried contacting someone higher up but it's radio silence. The temp manager said to wait until the 'rent due' amount was uploaded but it didn't load until today and now it's due tomorrow.

Thanks for reading. We've been trying to fix this for over 5 weeks and kinda at my ropes end with what to do next due to lack of management existing sadly.