Relieving Certificate

Sir, I joined LIC ADO job on 2nd December 2019 and we have to undergo two months Apprenticeship Period. I got a Stipend of 27000 INR. But due to my circumstances, I am unable to continue that job. Thus, I left the job and paid the Indemnity bond value of 25000 INR on 24th January 2020. They gave me the Photocopy of the Bill and said this is their procedure. After a week time, on 31st January 2020, they are releasing a circular like, "Candidates who leave the job within the Bond Period of 4 years should pay GST of 18% to the Bond Amount", this equals to 4500 INR. Till now I didn't paid the GST. Because, they didn't mention anything about Tax or GST to be paid in addition to the Bond Amount in any of their Documents like Official Notification, E-Mails, Letter of Appointment, Indemnity Bond, etc,. As I paid the Bond Amount one week prior to their GST Notification how can they demand me to pay GST of 18%? I think this is brutal and incorrect. As I left the job in the Apprentice Period itself and I got only Stipend not Salary, whether not getting the Relieving Letter from them will be a problem for me in my future Employment or is it Okay not to get a Relieving Letter?