vb.net Using SqlConnection doesn't free the file from use - vb.net

Question

I am working with a local .mdf file and I execute some queries to the database and I am using USING blocks to make sure the SqlConnection and SqlReader are disposed of correctly.
I then try to read the data of the file to generate a MD5 Hash of the file but it says the file is still in use.
The code isn't the cleanest it is my first time working with the Sql in a VB.NET app.
SQL Insert:
Dim finalW As String = ""
Dim finalO() As String
Dim currentcounter As Integer = 0
For Each Dir As String In System.IO.Directory.GetDirectories(Pathfinder)
Dim dirInfo As New System.IO.DirectoryInfo(Dir)
Dim temp As New List(Of String)
For Each currentFile In Directory.GetFiles(Pathfinder & "\" & dirInfo.Name & "\", "*.png", SearchOption.TopDirectoryOnly)
temp.Add(Path.GetFileName(currentFile))
Next
If temp.Count <> 0 Then
finalW = temp.Find(AddressOf GetNewIcon)
finalO = temp.FindAll(AddressOf GetOldIcon).ToArray
If finalW <> "" Then
Using con As New SqlClient.SqlConnection("Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=""" & PathFinal & "ImaginiDB.mdf"";Integrated Security=True")
con.Open()
Using cmd = con.CreateCommand()
cmd.CommandType = CommandType.Text
cmd.CommandText = "INSERT NewIcon (Name) VALUES ('" & finalW.Trim() & "')"
cmd.Connection = con
cmd.ExecuteNonQuery()
End Using
currentcounter = currentcounter + 1
Dim Id As String = ""
Using command = con.CreateCommand()
command.CommandType = CommandType.Text
command.CommandText = "SELECT * FROM NewIcon WHERE Name='" & finalW & "'"
Using reader As SqlDataReader = command.ExecuteReader()
While reader.Read()
Id = reader(0)
End While
End Using
End Using
For Each item As String In finalO
Using cmd2 = con.CreateCommand()
cmd2.CommandType = CommandType.Text
cmd2.CommandText = "INSERT OldIcon (NID,Name) VALUES ('" & Id & "','" & item.ToString.Trim() & "')"
cmd2.Connection = con
cmd2.ExecuteNonQuery()
End Using
currentcounter = currentcounter + 1
Next
Dim cur As Long = currentcounter * 100 / counter
SetProgress(cur)
End Using
End If
End If
Next
GC.Collect()
GC.WaitForPendingFinalizers()
SetLabel4Text("FINISHED IMPORT", Color.Red)
MD5 Generation ran after this process is finished:
Public Function GenMD5(ByVal Filename As String) As String
Dim MD5 = System.Security.Cryptography.MD5.Create
Dim Hash As Byte()
Dim sb As New System.Text.StringBuilder
Using st As New IO.FileStream(Filename, IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.Read)
Hash = MD5.ComputeHash(st)
End Using
For Each b In Hash
sb.Append(b.ToString("X2"))
Next
Return sb.ToString
End Function

Answer 1

So as mentioned in the comment by #jmcilhinney
Different connections use different pool as the MSDN says:
When a connection is first opened, a connection pool is created based
on an exact matching algorithm that associates the pool with the
connection string in the connection.
Thus I decided to implement the method:
SqlConnection.ClearPool(connection As SqlConnection)
I placed this just before my END USING:
Dim cur As Long = currentcounter * 100 / counter
SetProgress(cur)
SqlConnection.ClearPool(con)
End Using