I live in the UK & have an o2 pay monthly sim-only account, 10gb data, unlimited texts and minutes.
I use an unmodified samsung galaxy s10 android phone, originally bought in the UK from o2.
My partner lives with me & has an o2 phone-and-sim monthly package.
Neither of us have been abroad for over a decade.
Both phones & o2 accounts have been working fine with no issues for 3+ years.
For most of that time I've had 'forward on everything' set up for all but calls I've manually answered quickly, with the target for forwarding in all cases, my partner's phone number formatted as 07xxxxxxxxx
This has always worked well, such that whatever calls come into my phone, if I don't answer them straightaway they get forwarded to her phone, and she can take the call.
I've always been vaguely aware I'm probably responsible for the cost of the forwarded leg of the call, as if it were me myself dialling through to my partner.
I recognise that if someone were to call in from abroad, there might be a possibility the forwarded part of the call (from my phone to my partner's) could maybe be seen by the system as a roaming call itself - even though my phone to her phone would always be UK to UK. For years though, this setup seemed to work really well with all charges in practice covered by my allowances.
Just recently though I noticed my bill shoot up spectacularly. I had 3 calls within a week or two get forwarded through to her phone, which were subsequently identified on the bill as involving the USA and thus triggering some hefty roaming charges.
Each of the three callers were UK based, present in the UK, and calling from a UK number at the time. Neither I nor my partner (nor our phones!) have been outside the UK.
One was a UK BT landline, one was an EE PAYG user located permanently in the UK (friend in the same town), and one was a UK o2 contract user.
The only thing I have noticed is that since about last September, both my phone and the network seem to be increasingly formatting the numbers in international format, regardless of how they are stored, received as CLI, or dialled.
Before September last, everything caller ID was coming up as 07xxxxxxxxx. Now, virtually everything's being shown as +447xxxxxxxxx. In between, there seemed to be a very sporadic / random swapping between the use of the 2 formats, with the use of the international format gradually increasing over time.
This number formatting is just how the phone & network are presenting the numbers, it doesn't seem to be anything controllable within the phone itself (either mine or my partner's)
Only mentioning this in case there's a possible link between the use of international format on the network, and incorrect roaming charges (even though +44 still denotes UK?)
We both have data roaming turned off and neither of us have ever deliberately turned roaming on for voice calls (not to say it isn't switched on and we just don't know where to turn it off?)
Is there a rogue billing system out there that thinks if it sees a +, it's international?
I wondered whether anyone involved was using some kind of trick least cost routing service that made the calls seem to involve the USA, but I've dug quite deeply and this doesn't seem to be the case.
O2 did concede 'incorrect roaming charges' and gave a credit on my last bill, but I'm just worried about it happening again.
What could cause this?
