Dental procedure billed outside of dental insurance, now I may be on hook to pay for it

Last year, my husband went to a dentist office for preliminary analysis for tooth extraction. At that time, we had Anthem BCBS and my husband provided that insurance to them when they asked (along with the dental insurance info of course). Decided to do tooth extraction along with some tissue biopsy in February this year. I have no idea if they told my husband or not that this will be billed outside of dental insurance and to the medical insurance.

This new year we switched to Kaiser North California insurance HMO. Come February, tooth extraction and issue biopsy was performed (note – it was pre-approved by Delta Dental insurance) and I paid $500 on the day of service per pre-approved amount. Had back and forth with delta dental and we also go back some $120 after adjustments. Later in June, we got a bill from Dermapathology department from UC hospital asking to pay $250 for biopsy performed on the tissue that we had no idea about. We thought it was all handled by dental insurance. Since dental office had old insurance, the claim was denied by Anthem BCBS. We gave them new Kaiser insurance info in June.

I contacted UC billing department today and they mentioned because they are not contracted with Kaiser, they cannot submit the claim to them. I, when I check my Kaiser portal, I am showed that UC is in-network (but there may be a catch here – perhaps a Kaiser provider referral needed or only during emergency). Anyway, I was told that you should submit the claim directly. I am waiting for them to now send me the itemized bill in mail to submit to Kaiser.

Is there anything I can do here? The dental office did not explicitly told that they will bill medical insurance for the procedure. We thought it would be all billed to delta dental. Can I ask UC to bill to Delta Dental insurance instead if Kaiser denies it? Or we just have to suck it up and pay $250?