What to do if your cousin gives your father's name and number as a loan nominee w/o anyone's knowledge or consent? 🤬

My dad and his two elder and younger brother had business but that elder one betrayed my dad and younger uncle. My younger uncle goes on rickshaw to earn. And my dad continued his business somehow gathering help from his friends. My (chumtiya) cousin (Younger uncle's son) with whom we don't talk because he betrayed, shared confidential things with people (my dad's elder brother) who abducted my father's property and all the money he earned. He (cousin) always did this mischievous things like robbing, lying and went behind our back. He always changes his phones by taking loans or borrowing money from people and always fails to return it back. Few months back he bought phone and gave my dad's number as a loan nominee and since one week they are spamming my dad's phone with endless calls. He and that bank who made my dad as a loan nominee without his consent and knowledge. My dad doesn't even take his name because what he did was illegal, unacceptable and unethical. He hang out with that elder uncle and his sons who betrayed my dad even after my dad helped his father (younger uncle) for taking auto rickshaw and what not. Now he failed to recover the money so they are calling my dad to recover the money. Please tell me what should I do or what my father must do? Thankyou:)