Yeah, jobcentres do have individual phone numbers, you can look them up on Google Maps.
It needs to be the one your original appointment was at. The request goes from the Student Loans Company to the DWP who send it to a jobcentre. That jobcentre then sets up an appointment, which they can rebook.
Student Loans Company have to be strict about how many requests they send out to prevent national insurance number fraud. That's why once the request has ended up with a specific jobcentre, it is the responsibility of that jobcentre to do it.