Service bond

Hello My wife was employed in a private company in Bangalore whose head office was in Orrisa. The company had a service bond of 5 lakhs rupees and 3 years period. She has signed it also. She resigned at 1.5 years of her service and we paid 5 lakhs to get the reliving letter so that she can join another company in due time. It's been around 4 months and now since the background verification would have completed, I am exploring possibilities to send legal notice to the company to recover service bond amount we paid. Her package at the said company was 3.6 lakhs. The service bond agreement was signed by both the parties and there is no mention or signature of witnesses. Also, there is no mention of any reason whatsoever for the bond amount like employee need to pay because company paid on her training or tools or software licences used. There was no specific training which was done by the company. I have the original service bond agreement also. The service bond is on 10 rupees stamp paper. Please suggest here on the possibility of recovering the amount we paid.