Well, I changed my home Xbox by error and I lost my subscriptions.

You can contact Xbox and Microsoft at the link below and explain to them you made a mistake. They should be able to assist you in getting Live back onto the correct device.

https://support.xbox.com/en-US/contact-us

When you go to https://account.microsoft.com/ > Services and Subscriptions, does it still show your subscriptions?

The console that was your home console, was it another account's home console by chance?

Subscriptions are tied to accounts, and a home console is authorized with the usage license. You may just have to re-download your account onto the console.

I tried each and everything. I tried changing it at my hostel as well as at my home. I still getting that error.

Me and my friend got set our accounts as home consoles for some time(it all worked well). The error appeard when i deleted his account on my xbox as home console and wanted to change for anothers friend account.Now I can't set any account on my xbox as
home console and my friend can't delete my account from home console on his xbox . Messed up

i changed and lost my 11 months left of gold subscription !!!!!!!!!!!