That bank would have to offer the service for you to be able to check your account balance online. Look for a customer service phone number on the back of your credit card, or on your monthly statement you receive. If you have lost your credit card, find one of your past monthly statements for a phone number to call and report it. Also, refer to the Mastercard or Visa web sites for additional information concerning lost or stolen cards. We have no information other than this about lost or stolen credit cards.
Banks issue all credit cards, and maintain all credit card accounts.
Mastercard and Visa rely on their member banks to issue cards and set credit limits. You could call your customer service number, and ask for a lower rate. There should be a number on the back of your credit card you can call. Banks issue all credit cards for Mastercard and Visa. So you will have to contact the bank that gave you the application.