Standard bank collection department harassing us

Standard bank homeloans and collection department phones us 5 times a day, when you answer no one speaks if someone eventually speaks back they say we have missed a payment. When we requested for a email statement it took them almost a month too send the document. Once received we reconsolidate all payments were up to date, but collection department missed the payment reference and asked us resend the proof of payment which was done like every other month. This has been 5 months ago and they are still calling us. **** poor service