I have not pay for my account successfully and my credit card showed me that it is approved by them?

I applied a new card about 20 days ago and activated it as soo as i received it. And i added $100 to my account on the website. My credit card service  showed the payment was approved successfully but after several hours later the payment was cancelled by T-mobile. And i did it for several times in the after several days and all the payments were failure. So now i can use my phone and the latest payment has been always for pending. I want to know the reason. Thank you very much!