Hob says 'L' when turned on, tried solution but still not work

When I turn the hob on, it has 'L' sign.
Tried the solution offered which says it is childlock, but doesn't work.
When I press the front two '+' signs for a few seconds, it then turns off or sometimes turns to 'E', 'R', 'O' and 'R' in the four flashing lights. It then automatically switches off.

When I switch it back on, it says 'L' signs again

I have only had this for 2 1/2 years so surprised if it is already breaking

Thanks