The IAD-LAX segment of a flight originating from LHR was cancelled back in early Feb, and to my astonishment, as I was exiting the plane, the C-class FA handed me vouchers for a night at the Hilton, and breakfast the next a.m.
When I called the Hilton for directions there, they was about as frosty as the weather, claiming I had no such reservation, none was available and, I quote, "United knows it." Long story short, I paid for a room, brekky and cabfare from and back to IAD where the next a.m. I continued to LAX. The ticket agent at IAD counselled me to submit all claims to an address in Chicago--which, naturally I did within the first week after the incident.
I waited 6 weeks. then sent an e-mail to customer relations about the matter and received by snail mail within a week confirmation that my claim was being processed and I would "very shortly" receive a check fully compensating me--$200+, as I recall.
~ONE MONTH therafterl I received the check, NOT a UAL flight voucher.
It helps to be 1K, it helps to be friendly, polite, direct, plainspoken, unaccusative, focusing on facts and reasonable expectatons. I don't know what would have helped speed the process up. Good luck.