First check your CIBIL report if Simpl has an active loan account there. It might be of a different name depending on their lending partner.
As you mentioned you don’t have PAN, there is no way they can update your CIBIL report as they don’t have access. But if the account is visible on CIBIL, it’s in your best interest that you pay.
A friend of mine was in a similar predicament and he just switched off his number and moved on. Simpl did not report anything on his CIBIL.