I have that with my old phone, a Nokia E72. One Indian/Paki-run little mobile phone store here in Newcastle has someone who knows how to open it up and clean it for 10 pounds. Went to at least 5 stores before I found him, though!
(If Nokia would do it, I’d first have to take it to a service centre about 150 miles from here, it would take a few weeks and cost 70 pounds.)