Recovery raised by previous department after 03 years of Transfer to other department

Dear Sir/Madam, I was working as a clerk in a govt. institute 06 years ago. I was handling fees collection from students. During my service in the institute, I was couple of times maltreated by one of my seniors. 03 years ago, I was transferred in the middle of the session (Feb month) to other office....However post closing of the session in institute, my senior due to personal grudge got a recovery letter (1 lac plus) issued to me on account of lesser fee collected from students...In response, I replied them with facts that I had collected requisite fee from around 85% of the students and requested them to check their records and collect balance amt at the time of issuing No Due Certificate to students, if any difference is noted. Institute staff did not do any further correspondence.. Now after 03 years, when I requested them to issue me No Due Certificate further submission to my current office, institute staff is harassing me by not issuing me NDC and verbally asking me to visit institute again and again to clarify 03 years old issue. Apart from visiting institute multiple times, I have written couple of mails to the head of Institute to get me NDC, but nothing has been done even after 04 months of my request. Please advise me way out..