Hi raehos and welcome to the NS Community! 
First of all, I deleted your other (double) topic. I also deleted your picture because it contained your information. 
The travel expenses should be right on the cost counter. When you contact our customer service, they can’t directly see the total amount, but they can check all your journeys. It is not possible to pay this off before the invoice is made. You can wait for the invoice. Then we will try to take this from the linked bank account. If that is not possible, you will receive an email so you can pay as well. 

BUT the costcounter most often does not work properly-as has been reported here so many times that even staff should have gotten the message.

THE way to check what is due is via mijnNS=your personal account (though its likely in your case on that of the paying friend, access should still be possible). You have to open this via de site, not possible via app.

On the mail that is linked to it you will get a note that the bill is due and the total amount-plus the day that it will be taken from the bank. There are always a few days in between. Perhaps you can ask the friend to pass on this mail?

Hi, I already have money loaded on myov-chip card,,, cant you deduct money from there to cover part of my monthly expenses before using direct debit from my bank ?

When ordering an NS Flex subscription, the balance will be removed from the card when activating NS Flex at a machine (pick up order) and reimbursed to you via the next monthly invoice.

So, basically you pay the full first month, then get discount (the balance) the second month. Alternatively, you can get the balance back from a service desk at a station (before activating NS Flex).