I'm using a PAYG sim
I top-up
Phone works fine.
I let a month pass by without topping up
Phone WiFi becomes completely fucked up, it can find signals but cannot connect, I'd get weird errors like 'authentication failed' or just 'disconnected'.
I top-up again
Phones goes back to working fine as usual.
Can sim providers do this? I'm using GiffGaff btw.