This could be a case of fraud. Fraud is where a person obtains or tries to obtain property through some form of deception or misrepresentation. Currently the most common form of fraud is credit card fraud, where someone pretends to be you or uses your personal details to obtain cash or property.
You should immediately contact your bank/credit card company to stop your card and report the discrepancies. The credit card company/bank will have their own fraud department and will work in conjunction with the police. This means you do not need to inform the police as it will be done for you if necessary.
Have you been the victim of identity theft? Ensure personal and financial information is shredded or otherwise destroyed. Do NOT put such material in the dustbin or take it to the dump. See SQ506 for more information on identity theft and how to prevent it.
B rings up a mobile phone company and uses C's credit card details to order a top up card. B has obtained the top up card by deception. He has presented the card details to the phone company as if he has the authority to use them. The phone company would never have allowed him to have the top up card if they knew that he was not the card owner.