Harrasment from Collection Agents

I lost my Job due to which i wasn't able to pay my EMIs... i sought help of a Debt Management Company and their Legal Team Drafted Letter of Authority to the Nodal Officers of the Banks stating that the Debt Management Company has the Authority to Deal on my behalf. When Collection Agents reached out to me i have shown them the Letter of Authority and they would stop Bothering me. However Everyday i find New Agents from Kotak Bank reaching out to me despite showing LOA to the previous ones.. at the time of writing this there have been a total of 15 Separate Agents of Kotak who have reached out to me... 1) I want to know if the concept of LOA is valid or not because i noticed when i told the Agents about LOA they have no clue what that is 2) Can i take Legal Actions against Kotak for Mental Harassment for Hounding Me Everyday (Not Able to Focus on attending a Job Interview to get back on my Feet) when i have Communicated with the Nodal Officer of the Bank about LOA as i believe The Agents should have been made aware of this LOA and if they want upto date info then they should be reaching out to the DMC instead of me.