State Bank Of India [SBI] — wrong calculation of interest

Address:

Gauhati University, Kamrup Metropolitan, Assam, 781014

With reference to the subject above, i would like to state that i have registered a complaint on 24/07/2019 under the ticket number fd[protected]. The mail mentioned that complaint will be resolved within 10 days from the date of complaint registered. But when i checked by sms, it shows the ticket no is closed. But the issue is not yet resolved.
I have started a flexi deposit account on 23rd july 2014 which matured on 23rd july 2019 at 8.5 % interest. The day before it got matured, it showed a accumulated interest of rs. 56000 (Approx). But on maturity i got a interest of rs 14000 (Approx). I want to know on what calculation basis my interest was given at 3.5 % rate instead of 8.5 %. Am i going to get the reply through mail and will my issue be resolved or should i file an rti to get my answers or complain in rbi. I am clueless. Kindly help me and guide me to get my hard earned money.
My flexi deposit account no is - [protected]. (Gauhati university branch)-