According to the article dated April 19, 2017 on website of Tien Giang Tax Department: 

“A number of enterprises administered by Tien Giang Tax Department showed that recently, some people had posed on as Tax Personnel and called to notify the inspection plan for decrease the responsibility of violating tax law. 

Moreover, to take advantage of changing tax policy or through dialoge conference and disseminating policy held by tax department... some people had posed on tax personnel to threaten enterprises to buy tax book, training documents...

In the face of cheating action, to prevent timely violating the law, Tien Giang Tax department suggests enterprises to be vigilant over this behavior.

In case of receiving or seeing the informations of posing on tax personnel to come or call to enterprises, taxpayer should let the tax department know to solve the situation timely. Please call 0733.884.870 (tax inspection - Tien Giang Tax Department) ”