iPhone 7 has no service with various different sims from different service providers

My phone was on a pay monthly contract with Vodafone which ended a while back, I cancelled the monthly contract and signed up with Voxi. Since then the phone keeps saying its searching for network then ultimately it says no service.

I put the Voxi sim card into a different iPhone and its working so its not a sim card issue. I did a hard reset of the iPhone 7 and put in an EE sim and still no service, I also tried with an O2 sim and still no service.

Ive done a hard reset about 4 times and tries loading different iCloud accounts and still no service.

The phone is not Network locked either.

Anyone have any ideas why I'm having this problem?

It was working fine then when the pay monthly contract was cancelled them it just stopped working