Samsung S10 Invalid Sim

Dear T-Mobile...

I purchased a Samsung s10 a few months before, and I was using it on T-Mobile.

now I came back to India and when I inserted the Indian SIM Phone says Invalid Sim.

when I searched on Google about this, I came to Know its a Network Lock.

I found an application named as Device Unlock, I opened and Tap on Unlock, Then it not Unlocks.

then I searched online and found a few websites offering an unlock service for this problem.

they asking money for that. but when I bought the phone, the executives said T-Mobile will unlock it if I requested.

So, My Query is how to contact T-Mobile for this unlocking.

or

Should I go for the Unlock service offered by third party websites?

T-Mobile USA Device Unlock App - Official Device Unlock App

Kindly do a reply and help me to fix this as soon as possible.