That link is where they request correlation ID, and won't proceed
without it. However If you take the transaction ID obtainable from
Google pay history and remove any characters that aren't letters or
numbers (. and -) the form will accept the number...
Information for anyone else with this problem, Google claim that the
correlation ID required is NOT the transaction ID described above. This
is a mess where people get robbed and then our trusted corporate friends
at O2 and Google try and let it fall...