If they are shutting down towers/business without any communication/alternative to the customers, it will be a violation of license terms and covered under DOT TERM Cell's authority and you can register a complaint there.
Contact Details for Bangalore Circle:
Veera Gowda DDG
Dept of Telecom - TERM(Telecom Enforcement, Resource and Monitoring) Cell Bangalore.
Tel: 22372323 Fax: 22283355 Mobile: 9448010804 Email: ddgtermbg-dot@nic.in
"II Floor, Aminity Block, Palace Road,
Bangalore-560001"
For Karnataka Circle:
G Satyanaraya Reddy DDG
Dept of Telecom - TERM(Telecom Enforcement, Resource and Monitoring) Cell Karnataka.
Tel: 26651313/26637777 Fax: 26638888 Email: ddgtermktk-dot@nic.in
Ground Floor, Sanchar Complex, WMS Compound, 47th Cross, 9th Main, 5th Block, Jaya Nagar, Bangalore - 560 041
Also complain at http://pgportal.gov.in/ under Deptt of Telecommunications and continue approaching the higher appellate authority of TATA.
If they have decided to shut down CDMA in your area, you may not be able to stop them by doing all/any of the above but may get a clear answer what the issue is, whether a resolution is possible or not and accordingly plan your alternatives.