I made some changes in the function GetLatLong() that solve the problem in the south hemisphere, added local variable dNorth and dEast :

Dim dNorth As Double = 0
Dim dEast As Double = 0
' dblNorthing = If(utmL = UTMLat.North, dblNorthing, 10000000 - dblNorthing)
dNorth = If(utmL = UTMLat.North, dblNorthing, 10000000 - dblNorthing)
dEast = dblEasting
Dim arc As Double = dNorth / k0