How to access new mobile phone service. Help needed

My order for a new mobile phone service has been paid for and accepted. They have emailed me a QR code. i have no idea how to use it. they are v difficult to contact. i am going with a new provider, as it's cheaper for me.
i have screen shot the QR code and it now appears at the foot of my laptop screen.
the email said instructions would be there ? where?
there is a also PUK number in the email.
anyone know what to do ?
TIA (not aunt; thanks in advance).