My three sim is not working

[Noshanqazi]

I'm using three from last 5 months. I buy a new phone and my current three sim is not working on new phone but all other networks are working. Please someone help me. 

@Three1 

[MZone]

Sounds like the new phone is locked to another network or maybe doesn’t have the right frequencies to connect to the Three network. I tried my Three SIM in an old unlocked Nokia 6100 and it wouldn’t work either. Try going into a Three store for support. 

[sc1999]

From December 2021, all phones sold in the UK must be unlocked.

[sc1999]

What phone did you buy and where from?

[Paddiewack]

As has previously been said you must ensure your handset is compatible. Did you buy it new or secondhand? Please either elaborate as regards your handset on here or better still contact customer service of which this is not. 
333 for contract or live chat via the Three homepage for payg.