They don't have a public contact number (probably intentionally). When my SAR was overdue I sent them this and it came two days later.
Dear Sir,
On xxx I made a request for all data that the UKBA holds on me. I subsequently received a letter confirming my request, assigning it the reference DPU xxx. The cheque was cashed on xxx, but I have yet to receive the requested data. As it is now more than 40 days since the request was received, the UKBA appears to be in breach of the Data Protection Act 1998. If the requested data is not received within the next seven days I will lodge a complaint with the Information Commissioner's Office and consider legal action.
Sincerely,
If they still don't send it, complain to
http://www.ico.gov.uk/