I've had my mobile number for 25+years, been with Virgin for about 15y.
I have 3 x mobiles with virgin, mine plus 2 dc mobiles.
I also have Virgin media, telephone and broadband and have had for 12 years. Just as background.
I've had problems with the router for months now, I thought maybe from the storms, but it has not resolved. I phoned Virgin Sunday last week, bloke said nothing wrong with it (intermittant fault, difficult to diagnose etc...) and then said he could do a 'deal ' on my mobiles. (I get this a lot from virgin, you phone and they look at the deals and normally cut a few quid off) I said ok, he said he'd send me some SIMS, some details, some emails, change with in 28 days or you wil be cut off... I wasn't sure what he was on about, so cut the call short.
Few days later, Wednesday, I get 3 new O2 SIMS. I don' tknow what they are for, I phone Virgin, they put me through to O2. I am told that they only have 2 mobiles on the account and will give me PAC codes for them. I write the PAc codes down, then realise that if my DS2 has to change SIMs, i need to send this to him (he doesn't live here) and get him to phone and give all my details (as account holder) so i phone virgin again to cancel (within 14 days - as in law), get put through to O2 to cancel the porting. I get told the porting will be cancelled. Same day, virgin sell me a new 'deal' to £6 per phone, 3 phones, 12 mth contract. This is relevant later.
On thurday night I get a text from O2, saying they cannot Port on Thurs 31/3, it will be done on Friday 1/4 - I am at work Friday so ignore the text as being sent by mistake. Friday midday I lose SIM. 
Phone Virgin Friday after work, got put through to O2, ask why the porting was not cancelled, was told/'promised' that O2 would be reversed and my number returned to Virgin.
No SIm since then.
Spoke to someone at virgin yesterday, told by a manager that they couldn't put me through to O2 (against GDPR? Even though every single phonecall to virgin in the past week was put through to O2!) and they can't do anything as they don't have my number!
Phone O2 (on a 0334 number - is this chargeable?) - speak to someone who says I do not have a contract with them, they don't have my number, they can't do anything.
Virgin can't do anything as they don't have my number either. Even though they sold me a contract for 12 months on Wed, for my phone.
I don't know what to do now. I don;'t want to get a new SIM (I'm thinking of getting a Tesco one 
) but i've had the same number for 25 years! Everything is attached to it - all my authorisations for banking, my work pages, my email authorisations, all have my mobile number. not to mention all my contacts.
Any ideas what to do - I'm not on twitter.