What to do when tenant ignores you (aka landlord)?

[Eric W.]

Lol this tenant is doing lots of firsts for me. In 20 years a tenant has never ignored me. It hasn't been a long time but I expect a trend. It's been three days. I've called and emailed once per day. There are some things I urgently need to discuss with her. So what to do now? I suspect this may overlap with a 3 day pay or quit since she may be ignoring me because it's nearing that time of the month. But let's ignore the pay or quit for a moment. Back to the ignoring me. So should I certify mail something to her? Post something on the door? Or what? Thanks!