IT'S MARY-SAN. I'M IN ANOTHER WORLD NOW...

It's Mary-san. I'm in another world now... summary:

Naibara Hirokazu moves from Miyagi to Saitama to start university in Tokyo. Not long after settling in, he starts receiving eerie phone calls from an unknown number. A girl’s voice whispers, “It’s Mary-san. I’m at the garbage dump now… I’m the doll you threw away…” Brushing it off as a prank, he hangs up—but the calls don’t stop. Worse, the caller seems to be getting closer.
The next day, he answers again. “It’s Mary-san. I’m in front of your room now…”
Could it be that Mary-san, the infamous urban legend, has been isekai’d—and now she’s asking for help over the phone?!