Harrassed by incompetence

Incredible Connection 30 month account is paid up to date as of 25 June 2015. This was also confirmed instore at one of the JD branches. Since September I have been getting calls from JD Financial Services saying I owe them unpaid instalments. I am now being harassed with 3 calls per day, despite logging an enquiry (which has now been rejected). Just received a call from a very rude young madam by the name of EC Rudaiba (she refused to give her name however and dropped the call) who told me I must listen carefully. This is the final straw. What must I do now as this is menacing harassment, and nothing is taken seriously. They never answer their email inbox so the only option now is to visit my attorney to stop this once and for all!