How to remove a credit card from the in-app billing feature?

All I wanted is to try out the in-app-billing of my app (which is still quite a mess to deal with, post here if you can help making it easier) .

So since I can't try it out on my own account, and because I have only a single device, I've tried it out on my work's "fake" (not fake, but doesn't really belong to anyone - all workers use it) account and added my own credit card account to it (otherwise it won't continue, even though it is in the test group of my app).

All went well (I have some bugs but I will fix them later), but now I want to remove the credit card from the account, but I can't find where I can do it. Not only that, but it doesn't even ask me for a password for the app.

All I see on the app itself is this:

I can only add more credit cards. Long clicking didn't do anything. No way to remove credit cards...

I also tried to make a "wallet" account here (going to "payment methods") , but it doesn't show any credit card:

I've even tried to install the "wallet" app, but it doesn't let to install it (says "This item cannot be installed in your device's country.") .

I've also tried to find any way to delete the credit card on the play store app and website, and to clear the play-stop-app's data and the google-play-services-app's data. I've also tried uninstalling the app i've made, and of course restarting the device.

Nothing helped.

ok, this is a stupid mistake, which I've found while talking with google's wallet support :

the device had 2 accounts, and i've looked at the wrong account (the second one), while the credit card was attached to the first one.

then, on the website of the wallet service, I could remove the credit card.

I wonder though how it should be done within the Android device, without the ability to install the wallet app.