It's imperative that you read the lease very carefully, with special attention to the paragraph regarding utilities.
If you signed the lease, you are bound by the provisions of the lease, no matter what was told to you verbally.
Hoping that your lease is explicit and clarifies who is responsible for what.
When you say that they are not separated, do you mean that all shows up on a single bill ? Or that there is actually only one meter for each ?
Are there individual sub-meters for the utilities? If so, it's extremely easy to determine which unit used how much of each utility. If the units are not sub-metered, it means that you only have one gas meter, one water meter, etc. for the entire building. That will be impossible to determine which unit used how much water, gas, etc.
Re your requests to the property management firm, keep a timeline of all conversations, persons involved, etc.
Keep detailed records, and put everything in writing.
Here's a link that you might want to look at: http://www.dca.ca.gov/publications/landlordbook/catenant.pdf
Here's also the contact details for San Bernardino County
SAN BERNARDINO COUNTY
Inland Fair Housing and Mediation Board
560 North Arrowhead Avenue, Suite 7A
San Bernardino, CA 92401
(909) 888-3763 (800) 321-0911
(909) 972 1616