Can't contact/select RTC clinic

My GP said they were referring me to Harrow Health, and I got a message on the NHS app telling me that I had to still select a clinic (with only the 1 option of Harrow Health). However, it says that to book/select the clinic, I need to contact 0000000, which of course, I can't do.

I went to the Harrow Health website, but they request that their phone number not be used for contacting them about ADHD services...I also went to my GP again but the receptionist told me to call a number that is the mental health crisis line for my area?? So I'm not sure I should use it.

I'm just so confused at this point about what I should do to just make sure the referral goes through.

Has anyone experienced this? Should I just call the Harrow Health number or the one the receptionist gave me anyway?