Hi there Hesseleitt
This is a very unusual situation. Are you sure the card was included in the bankruptcy? If for some reason you forgot to include it on your bankruptcy statement of affairs document, it may have been missed and remained active throughout your bankrupty.
If you have now been discharged and the card is still active and you are using it, you are actually not doing anything wrong. Now you are discharged, you are allowed to take credt again if anyone is prepared to give it to you. As such you can use the card as long as you are making the minimum payments required. However, I would recomend that you dso not use it unless you pay the full balance off each month.
You mention that you believe that you now have a good credt score. I am surprised that you think this as the record of you having been bankrupt will remain on your credit file for six years from the date of your bankrutpcy. This will generally mean your credit score remains bad for at least 2-3 years.
Have you applied for a copy of your credit file to check?