Daily harassment from the Call Centre

I have made an arrangement with MDB for monthly installments and have honoured that arrangement monthly. I been contact with a settlement offer which I declined as it is not financially possible and we concluded the discussion on a positive note. I am still being phoned every day by the call centre and I assume they are then charging my debt with this call and admin fee so they can generate revenue. If they do not stop phoning me I will be blocking them via Truecaller. We have an agreement for the next 12 months, now leave me alone or I will take further action around harassments with the ombudsman.