Unfounded payment

I missed my payment Date with this company and paid them a week later by making a bank transfer on my spp . They have been calling me about payment reminders from legal firms . I've sent countless emails with proof of my payment made to them but no response. Sent copies to the info department but the loan still remains open . Logged complaints but nothing seems to happen . I can't cancel the direct at my bank which has also been of no assistance whatsoever . Still this company sends me threatening reminders of payment not being received when I paid them in full .