Shares of digital payments firm Paytm tumbled 20% on Friday after a central bank clampdown on its payments bank continued to weigh on investor sentiment despite the company's attempts to assuage fears of a hit to its business. Paytm shares were at 487 rupees, their lowest in more than a year, at the bottom of an exchange-imposed trading band for the second day in a row. Shares of the company are now down 36% so far this week.