I am well aware of the rules.... no need for any attribution ;)
*from the freepic website:

i use standard icons and vectors all the time in my contest designs...
Designing from scratch for a contest is not always economically realizable (i need to work for money too)
Final designs will always be altered or finetuned as the 'client' wishes in case they decide to go with me...

Edit: Freepik's resources for commercial purposes