There are lots of posts at the moment about payments - and obviously a lot of people are in a similar position - the advice is contact O2 and speak to them.
I have just done this myself, and I was offered a payment extension to the 19th of this month (which should be fine for me) without question I was also advised to contact them again if I needed to extend this. In the meantime no restrictions will be placed on my account - but I may incure the £3.50 late payment fee and the obligatory warnings about credit history apply.
So O2 will help if they are able to - you need to call them and unfortunately persevere with their high call levels. Obviously this is on an account by account basis but it seems they are doing their best.
You can reach the Payment Management team on 0800 902 0217.
The opening times are:
Monday to Friday – 8am to 8pm
Saturday – 8am to 6pm
Sunday – 9am to 6pm