Surety/ Guarantor for Chit fund

I have given surety to my sister for a chit fund sum of rupees 5 lakhs which was to be recovered in 40 months with the instalment of rupees 12500/- per month. She paid instalments for 18 months. Chit fund company has given Case in jt registrar office and the award was passed U/s 71(a) of the Chit Funds Act,1982 to recover the amount of rupees 3,33,312/- from the Opponents. Order was passed on 10/02/2016. 02/01/2019 the advocate of Chit fund company send a notice to my society and requested them not to permit any type of transfer/ gift/ mortgage or permit any change of title of my flat. At present my sister has registered a case against chit fund to reduce the amount to be paid and give option of paying the amount by monthly as the Chit fund was demanding to pay the full amount in one cheque. I am in need of money for my sons education for which I got a mortgage loan approved. When I ask society for NOC for the mortgage loan society reduce to give NOC as Iam surety for the chit fund matter. Please advise me to get a genuine solution for getting the NOC. Regards S.S MENON