Poor customer service and account department

My loan with them was approved in January. Our contract stated that first payment will be end of January, as this is my salary date. They deducted the money on 26 January. I disputed this and then paid them again on 31 January. Since then they have been sending me sms's and emails that my account is in arrears. I have spoken to several call centre people and each time they tell me my account is fine and it will be updated. this month again they contacted me and asked for my bank statements as proof of the payment made on 31 Jan. I send them the statements on 5 June and I have not heard anything back yet. It has not been addressed or updated at all and still I am getting threatening messages. I am so frustrated and annoyed. I ask them to phone me, and they never do. I have no idea how to handle this further.