Then, 2 option:
1- disregard the site's schedule and confirm on phone who's there.
2- disregard the agency entirely.
You can't get them to change the site schedule if they don't feel a need for it or if there's technical reason. There's only the 2 option above I can think of. If you're a regular customer but stop calling because of the site's schedule, then you have some weight but, beside this, it's up to them!