Getting different information about coverage from Medical Group vs. Insurer (Bay Area, CA)

Hey all- hoping to get some advice about an issue I’m running into

I started a new job and am being offered two plan options: 1) Kaiser HMO 2) United Healthcare Select Plus PPO

My current doctor is not within Kaiser, so ideally I would choose United Healthcare if they are in network. On United Healthcare’s website it states my doctor is, and when I called United Healthcare they confirmed their current contract (as did the broker for my employer’s plan).

However, when I called my doctor’s office to cover all my bases they said they don’t accept that United Healthcare PPO, only HMOs. When I called back the next day the person I spoke with said that was true for new patients, but as an existing patient I “should be fine”. When I asked what that meant they essentially said it was above their pay grade lol (which like, I get it but I also need this info…) My current provider’s website also does not list the “Select Plus PPO” on their website as a covered plan. However, the same webpage instructs you to call your insurer to confirm complete coverage information.

I feel like I am getting two very different answers and don’t know which to take as truth- I don’t want to sign up for a plan only to find out my doctor is not in network. Wondering if anyone has run into a similar issue and whose response holds more weight?

Any insight/advice would be appreciated- thank you