It's a public grievance portal where you can register your complaint with the respective authority. In this case, the complaint goes to TRAI and then to BSNL, they'll quickly resolve it. Go to https://pgportal.gov.in/ and select the appropriate category and register a complaint stating that BSNL staff is refusing to change the plan.
Make sure to enter the proper plan details such as plan name and fees. Also mention the previous plan details and the plan you would like to change along with account details.
Make sure to enter the proper plan details such as plan name and fees. Also mention the previous plan details and the plan you would like to change along with account details.