Can't receive calls or send MMI codes

[PDDobster]

I can't receive calls, and when I send a MMI code (e.g. *#10# or ##002#) I get "Connection problem or invalid MMI code."
I can send calls, and I can also send/receive texts fine.
Using my previous phone also yields the same results. Same with turning off my wifi.
I don't have wifi calling as on option in "My O2", and my phone is just a standard unlocked phone. 

Any help would be appreciated!

[pgn]

PAYG and MMI codes are hit and miss, as PAYG does not support certain advanced network features, like call diversion, etc.

A lot of the stuff that needed MMI codes has now been moved to My O2 app for Contract users, eg adjust number of rings before VM answer, call diversion, etc.

Does your PAYG MyO2 let you see anything that may help? Note the App and Web versions of My O2 can differ in this respect.

Stepping down to 3G in your settings sometimes helped, but 3G may already be gone where you are. 

WiFi calling has yet to reach all O2 PAYG customers yet, not that you had it on anyway.

Have you turned off Voicemail, Guide: All you need to know about O2 Voicemail 901 ?

Also for balance queries: https://www.o2.co.uk/help/account/billing-and-usage/checking-your-pay-as-you-go-balance

What are you trying to do, exactly, @PDDobster?

[PDDobster]

I'm just trying to be able to receive calls again, and it's what I tried before posting here as those seemed to be common things to try for the issue I am having.
I haven't turned off voicemail, but I doubt that would be an issue as I haven't changed anything with voicemail for years.

[PDDobster]

Oh, I forgot to mention, I don't have barring and call diverts available.

[PDDobster]

It is entirely possible that I didn't realise that the check balance MMI code was changed/removed, and is a non issue.

[PDDobster]

Never mind, might've just been the network being weird yesterday, I can receive calls fine now.
Ty for the help regardless.

[pgn]

You're welcome, @PDDobster.

[Spindle]

The check balance code *#10# still works fine for me?