When should you require to be addressed by your title?
A lot of admin documents are produced by machine these days, the ones that aren't are usually done by clueless people who aren't paid an awful lot. It would be ideal that they addressed you as 'Dr.', but unless they deal with a lot of doctors they probably just shoved your name into the standard mail merge template. 

If you'd rather be addressed as 'Dr.' then raising the issue with them wouldn't be stepping out of line, after all you are the one providing them with a service.