Winner activates, doesn't mark as received.

Maybe try to post something on their profile, or contact someone from their friends list and explain why youre bothering them.

wait 2 or 3 days and if the winner still doesn't mark it as recieved report him

Had that once, didn't mark it for 2 days, posted something here and instantly it got marked.
So might help. :p

wait 7 days and create a ticket to support... also blacklist this dude or fem-dude. but don't create topic like this piece of horn(or something else) scum me. blacklist him. it's more likely will lead to blacklist you by community. so if that not Troll topic or hidden giveaway so what you gonna do. good luck then.

He has 7 days to mark it received.I had a winner who had 3-4 unmarked wins, but before the latest one would get older than 7 days marked all BUT ONE marked. I don't know, some people are just loving making a mess around them and make the easiest actions in the possible last minute... don't know why it's good. I'M also quite a terrible procrastinator, but this is annoying even for me.

they have a week to mark. even if they activated.. so unless a week has passed, don't contact support.
after a week (from the GA ends) contact them.