About timebounds-promotions of pu lecturers (karnataka)

Respected Sir/Mam, I am working as a lecturer for PUC in a Aided-institution from nearly 20 years(KARNATAKA).As i belong to ST category, nearly 10 years ago,Institution management offered me Principal post as a promotion without any particular roaster(they said,they came to know orally from PU board about the promotion, without any hard copy).Then,they asked me the willingness to take promotion or not,they gave me 3 days time.Finally,they pressurized me and made me to give up the promotion and they took my statement on 20 Rupees stamp paper. Again 5 years ago,they made the same thing again.But, they never asked willingness for others, who got promotion as principal now. Now the management said,i am not eligible to get 20 years time bound(i.e, increment) as i refused promotions as per KCSR rules and they sent requisition letter to board to clarify about this.They didn't mention that they asked my willingness.But,they've sent only my statement of refusal on 20 rs stamp paper.Now, the board PU board replied, that i'm not eligible to get 20 years time bound. I'm willing to file a case in KSAT(Karnataka State Administrative tribunal). Now my question is, 1.Is there any law to ask willingness of the Lecturer,about his/her promotion to principal post...? 2.College management offered me principal post without a proper roaster... is this a correct way? 3.and they made me to give a refusal statement in 20 rupees stamp paper.... is there any provision to do so? 4.If i file a case in KSAT(Karnataka State Administrative tribunal) about this, what will happen? Do i get my time bounds approved? or Do they promote me to principal post? Is my appeal valid or not? Shall i appeal to KSAT(Karnataka State Administrative tribunal) or not? Thank you.