Double Debit still getting harassment phone calls from RCS

My Account was double debited on 25 October 2018, when I realized the anomaly I called RCS who acknowledged the error and told them I would reverse one of the debit orders. Now I am getting harassment phone calls and letters, even though the account was settled for the month in full. On the 12 Nov 2018 I received a letter of demand , when I called again, there was still an acknowledgement of an error of which nobody is bothering to fix. few minutes after calling I still got a harassment phone calls from the same RCS agent.

What need to happen is for RCS to compensate me for the unnecessary debit and my reversal for an unauthorized debit. RCS is now refusing to pay for the charges I incurred due to debit issue "We apologies for the Error but you will not be receiving any compensation" . I need my money for you incompetence and will be waiting for an apology.