No 4g on new samsungs

[tomm2000]

On a voxi sim only deal. I have used the sim for a few years in refurbished phones to keep the cost down.
 I've gone from Samsung S8 to S10 to Pixel 5 with no issues at all. 
 Thought I'd move to a Samsung S21 but no matter what I tried, I could not get 4g... just stuck on really slow "H" status.  Checked APN settings many times. Factory reset.  New sim.... Nothing worked. Yet I can pop the sim into any of my older phones and the signal is great again. I put it down to the mobile so returned the S21 and got a S21fe instead.... Same issue.. No 4g or 5g!
 So I'm stumped again (as are voxi customer support ) I'd love to get the S21FE signal working as well as it does in my older phones. Could anyone point me towards something I may have overlooked in the settings to solve this please? 

[AnnS]

It there under mobile networks @tomm2000 

You are using the SIM in slot 1? Take the phone into a Vodafone store for help. 

[tomm2000]

Network Mode is not under mobile networks.

I have 

Data roaming 

Enhanced calling 

System select

Access point names 

Network operators

[AnnS]

Have a look at system select and see if it's listed there. 

[tomm2000]

No it isnt. 

[tomm2000]

The s21 and s21fe were refurbished models from amazon. Do you think I could have ended up with foreign models and if so how can I check? 

[AnnS · Accepted solution]

The phones are not UK specification, probably EU, Return the phones you will never be able to use the UK 4 and 5G network. 

A Vodafone store won't be able to help.

[BandOfBrothers]

@tomm2000 even if the phone is a grey import they will have the bands and frequencies to work on all uk networks. 

The only issue can be is 5G sometimes. 

[chistery]

Try dialling: *#*#4636#*#*

Do you see phone info  / Set preferred Network Type?

what's it set to?

[tomm2000]

I get the message "number not valid"

I have read that it doesn't work on some Samsung mobiles 

[chistery]

Download the Google phone app and try it in that dialer.