SCN ISSUED FOR EXTENDED PERIOED - Service Tax

An SCN (Show Cause Notice) was issued for the Financial Year 2014-15 on September 20, 2020. The SCN was issued due to a mismatch between the 26AS and ST-3 return . The assessee has filed a NIL ST-3 return and has not recovered any service tax from the customers. My question is, whether the period from April to September 2014 is already time-barred? Can the department invoke the extended period in this case?