Replace Comma In String But Only At Specific Position

I am reading a csv file in VB.net and saving the line to a SQL database. At a later point in my code, the SQL line is retrieved in the application, and the Split function is used to get 'field' values. The Split is done taking comma as the separator. The application processes many other files (including excel), and the split function is used for all of them. The problem I am now facing is that one of the csv files I read, has a field value that starts with " followed by multiple values separated by a comma and ends with another ". The normal reading of the csv file results in each of those single field values is taken to be a separate value.

An example line is:
Elker,MissB,"Bus, Taxi, Train, Ferry, Parking, Toll",800253
Where there should only be separated to 4 columns, they get separated to 9 columns instead. What I want to do is replaced the commas after 'Bus' and until 'Toll' with a '?' instead. I have tried using Replace, including the overloaded one with starting position, but it ends up replacing ALL the commas in the line with '?'

Attempt 1:
If vstrLine(intStartPos) = "," Then
strRetVal = Replace(vstrLine(intStartPos), ",", "?")
end if
Where vstrLine is Elker,MissB,"Bus, Taxi, Train, Ferry, Parking, Toll",800253
and intStartPos is the first instance of a comma after the "
It returns only the '?' and not the string with 1 comma replaced by '?'

Attempt 2:
If vstrLine(intStartPos) = "," Then
strRetVal = Replace(vstrLine, ",", "?", intStartPos)
end if
It returns a string with all commas replaced with '?'