I have just recovered my sim to a new smalled nano sim because I was unable to find a phone that takes the size sim I had which was at the time, the smallest, but seems that manufacturers have decided that
nano is the new small but do not offer multiple sim slots to allow older cards to be used in the mobiles as a transition option.
So I have had 7 days nearly of no phone, internet or access to anything that would allow me to log in to my giffgaff account like the two tablets that kep[t on being refused login, I ended up carting my compute a mile up the road to use my friends wifi on my PC as its password saved on my PC, that is the extreme I had to go to to be able to do a sim swap with a sim card that I happend to have on hand, and then go back online just this minute.
This was not helpful given I needed to log in to my giffgaff and despite my attempts, got told to wait 30 minutes, which is not helpful, if the system can pick up on this and time me and others out, you should be offering up a support ticket and ask the phone number and a message field that would have allowed me to say from my tablet that I can't log in, my sim card is too big and can't be cud down any further and I need a new sim card of the nano variety. IT would have solved a number of problems as you would then know I need a sim swap, that I am lacking internet is als anther indicator, all too often it is assumed that people can easily access the internet.... HELLO...!!!! Try going through what I went through, the system you employ, whilst pretty rigid in security, lack much for people in need of assistance who can easily be verified as a customer from information that is given and that it should be a limited assist with things like sim card problems.
So when I resorted to traipsing a mile up the road with my PC to solve this, I was able to get the sim swap sorted, all attempts before had failed and despite providing a previously used login password, it in itself should be indicator that I am very likely
the account owner could also have emails sent out to be confirmed as part of a course of assistance.
This is something that you should look in to and should only be an option if it is a sim problem and that the user has failed to login, could state their issue and get some assistance because of the type of help is needed.