There are two separate fees you might have to pay when applying for a Canadian visitor visa.
The first is the application fee for the visa itself. You pay this online directly, when you apply online for the visa. This costs $100 CAD.
The second is the $85 VAC biometrics fee. You pay this fee only if you need to visit a VAC to give biometrics in order to complete your application. You also need to pay the VAC fee if you submitted a paper application through the VAC instead of submitting it online. In this case the VAC will collect both fees.
Finally, the VAC may add its own service charge onto the top of the above fees.
If you are not a national of one of the countries from which Canada requires biometrics, you can apply and pay ($100) online, and should not need to visit a VAC; you will deal with the visa office directly.
In your case, it appears that you are not a national of one of those countries, and you have already paid the visa application fee online, so you only need to mail your passport to the visa office.