Is that true O2 does not support call forwarding on One Plus 6 handsets?

[samsg30]

I own "OnePlus 6" handset and recently moved from THREE mobile to O2 and noticed Call Forwarding cannot be setup now which was working fine with Three mobile.

I get 'Unexpected response from network' error when trying to setup call forwarding. Upon calling O2 customer service, I have been advised they don't support OnePlus handsets which seems rather strange as it does work with Three mobile network atleast. They don't have any technical reason as to why it is not supported and I really need this feature since there's no mobile network in my office so I end up missing all calls if call forwarding can't be setup to my desk phone.

Any reason why O2 doesn't support this particular handset or way to set this up?

Thanks

[MI5]

@samsg30 

You'll need to disable WiFi calling to setup call forwarding.

WiFi calling can be enabled again afterwards but it's a bit off a faff if you intend doing it often..

[MI5]

Alternatively, use WiFi calling when in your office assuming you have a WiFi network there.

[samsg30]

I looked at thread and wifi calling is off already and followed all the steps mentioned in the thread like calling O2 to disable wifi calling too.

Their response is this particular handset is not supported 

[MI5]

I don't believe their response! How many SIM slots are you using and which slot has your O2 SIM ?
I can forward between my SIM cards or to a landline so it is a supported handset, not that handsets need support for call forwarding anyway!

[MI5]

If you have a spend cap, this can also have an effect on some network features and also doesn't work on PAYG but that shouldn't be an issue to you.