How do I delete my credit card information from Facebook Ads?

[Kiran]

It so happened that I thought of making use of a Facebook Ad coupon that was sent to me by email (worth $25 free) for paid advertising on Facebook. Since it was free, I thought of venturing to see how it would work. But while placing my Ad it asked for my credit card information and also mentioned that I would only be able to take the benefit of the coupon if I enter my valid funding source information (i.e my credit card information). I did so and for the first 3 days I was able to take the benefit of the coupon. I assumed that I would be notified from Facebook or they would rather seek permission from me to use the funds from my account if the coupon expired (which all on-line campaigns would do),...but they didn't.
To my shock I see, the very next day I was charged $30.
I got very annoyed after this, and so I logged into Facebook and deleted my Ad Campaign immediately. But now again after 4 days I see I've been charged $3.50 from Facebook for no reason (even after my Ad campaign was deleted).
Now I seriously didn't know what to do about it.
I called my bank and they say that it was authorised since I had provided them my credit card information. They advised me to go on Facebook and search for an option which would allow me to delete my credit card information from Facebook.
So went to the billing section on Facebook Ads, I clicked on Funding sources and while searching for an option to delete my funding source information, I got this saying -- 'You cannot edit or remove your primary funding source. In order to remove this funding source, you must first make another funding source the primary source.'
COULD SOMEONE PLEASE help me out over here?
I don't know how much money am I going to lose like this?

[CJ]

Cancel your credit card.
Anything you get in an email asking for credit card details you can safely delete.

[Mr. Man]

You should call the Facebook people and talk to them about it. Or just cancel your credit card so they will have no way of withdrawing money from your account. I myself have never invested in an add or purchased anything from Facebook in my life.