Not responding to e-mails

After numerous e-mails sent regarding my statement of account, I still had no luck with an answer. I settled my amount in full, after my account was settled they still raise interest. How can you raise interest on an amount settled. I have asked them to explain this to me, They are not responding to my e-mails and I am afraid that they will raise more interest at the end of this month. Very disappointing as they don't even have an automatic response to e-mails.