3rd party OS Linux upgrade folly

I use a dell inspiron 660 that i purchased on line. It had win 7 installed. replaced win 7 with <Not supported by Dell. DELL-Admin> Linux Mint. Computer happy system, no conflicts. I purchase an upgrade 4rm ebay seller. That mixed win 11 with linux. locked me out of any policy edit. Controls what sites i can see on line. what i can download. restricts, hides & removes all root control, i can change, delete ANYthing! changed the bios 4rm Vostro 2 Aptio. I tried 2 reset, couldnt. told seller wanted money back & to get their stuff off my pc & was I threatened. all i did was tell them how their usb messed up my pc. was not derogatory or use bad words or 2 replace my pc. just refund & uninstall. bank, email passwords all compromised. Maybe even my apple imac. My dell pc was healthy. I only wanted 2 upgrade. I havent messaged them back i want 2 tell them some choice words. but I did nothing to the seller that would warrant such a threat. so still still i sit and dont know what to do. This seller did not sell me linux & I bought the software & should have the same licenses rights, accessibility & control  as the seller & dont. I know C++ is MS why is my linux os full of C++ & win apps Really well done, nice graphics & layout. Very quick But I prefer privacy &most of all FREEDOM! & my pc told me there was unauthorized users as well. I feel walked on and stupid. I think my rights were violated. their software infected from the bios up.  I cot sick of seeing a file that loads early in the MBR and can inject yadda.