Frustrated with call center agents.

Bad service from call center agents. Called on the 13th May to close my account(credit card) was told all fine and account can be closed. Now interest is still been charged. So yes I most likely should have asked for a settlement(slipped my mine) but shouldn't the agent have informed me then and advised me of my error. Now the blame is fully on me. No customer service. What happened to the saying the customer is always right. Oh and when you want to speak to a manager, forget they apparently can't transfer cause they working remotely. But however I was transferred from the 1st agent I spoke to another agent.