Account duplicated and handed over for collections!!!

I have a revolving loan with Standard bank for a number of years. My account has never been in default. During the lockdown I made arrangements for a payment holiday. According to my statement I have made payment until the end of April. I received calls however from the beginning of the month of July from a collection agency named Shackleton Credit Management. At first I told the agency to fly a kite due to knowing that my account was up to date. After which I called Standard bank to report this mess. The person from Standard bank called me back and advised me to ignore the calls. This has now escalated into full blown harassment from Shackleton Credit management. I have had heated arguments with their agencies trying to defend myself against a mistake that was made by Standard banks legal department. After my call to Personl lending Collections this morning, I have been informed that I have the same account number which is duplicated with two seperate references of which one is up to date and the other handed over to SHACKLETON CREDIT MANAGEMENT!!! How is it possible that Standard bank hands over an account which firstly is not in default, and if it was, made no attempt to contact me! How is your contracted company allowed to harass me? 18 calls from this company in a matter of 10 mins. I am not happy with the kind of treatment I am receiving as a long standing client of Standard Bank. This is demeaning, degrading and an insult.