What are the laws regarding credit charge-offs and collecting interest?

Collecting interest on debt is generally governed by state law. There is no correlation between charging of a debt and the creditor's right to collect interest. After 180 days a creditor will "charge off' an account that is deemed in default. Interests and penalties will continue to accrue until the account is settled in some way, such as paid in full, a settlement agreement, and so forth. Although credit card debt is considered unsecured debt, this does not mean the lender cannot employ legal remedies.