Lena, Ernesto and the madame

I'm a little confused about something. Toward the beginning of the film, Lena is working for one of Ernesto's companies - as his secretary, it looked like. But when her father gets sick, she suddenly needs more money, so she calls a woman she used to work for, a madame, to get her hooked up with clients quickly. Later that evening, Ernesto calls her at home as a client of the madame's business. Apparently Lena recognizes his voice (he doesn't identify himself by name), because she terminates the call quickly. Then she calls the madame back to yell at her for giving out her home phone number to Ernesto, because "that's not how it's done".

Question is, how did Ernesto know that Lena was looking for clients just then, and from this woman? Even if he'd researched her history, knew she'd been a prostitute and who she'd worked for, how could he know that she was going to call the woman that evening to request a few weekend clients for extra cash? That is too much of a coincidence. And did he know who he was talking to? She was using a pseudonym, but he certainly seemed to know who she was.