Most likely, you have selected 4 (or more) allowed sessions in the Settings section of your personal account, which is why the package cost is increased 2 (or more) times.
Set 2 allowed sessions and then you will be able to buy a package.
Remember that we also use the Time-based payment scheme, where you can watch even 20 channels simultaneously. Money will be deducted from your balance for the actual viewing, not for the number of allowed sessions.
