None existant service!

Good day, trying to resolve a payment mistake with you is an absolute & total nightmare. We logged a request on 14 Aug & no-one reverted to say we needed a letter. We called, Sales Area Manager emailed & called, we called again & again & again but no response. No reply, no phone call, no sms, nothing! Does your credit control department exist? Do they do any work? Do they actually read emails? I doubt it! What will it take to get this payment sorted out?