Question about therapy billing codes (90834 vs 90837) – how to make sure I’m being billed correctly?

Hi! I just want to make sure I’m understanding therapy billing correctly and would appreciate some input.

Before starting sessions, I asked the office about out-of-pocket costs. They told me:

• 90834 – $121
• 90837 – $147
• 90791 – $150 (intake)

I had my intake session (90791) and then my first regular session after that. I noticed my second session was billed as 90837 ($147).

From what I’ve read, the difference between 90834 and 90837 is session length:

• 90834 = 38–52 minutes
• 90837 = 53+ minutes

My understanding was that my sessions are scheduled for 50 minutes, so I anticipated being billed 90834 unless we went over 52 minutes, which I get can happen.

For my second session, my therapist was about 10 minutes late, and we ended about 10 minutes later than the scheduled end time. I didn’t think we went over 52 minutes of actual session time, but I wasn’t timing it closely.

I just want to understand how this works and make sure I’m being billed appropriately in my future sessions

Is it reasonable to ask my therapist to clarify which code she plans to use for our standard 50-minute sessions? And is there a tactful way to say I’d prefer to keep sessions within the 90834 time range unless clinically necessary to go longer?

I don’t want to seem difficult, but just want to make sure I'm understanding, because it's expensive!

TL;DR: Therapist quoted 90834 ($121) for 50-min sessions and 90837 ($147) for longer ones. My second session was billed as 90837. Is it appropriate to ask how session length is being determined and request staying within 90834 time if possible?