Sims freeplay quest the lost artifacts not working

I'm on the raiders of the lost artifacts quest and I have to find the third artifact. I went swimming in my neighbours pool and I found some graphite. Then I went to the mysterious island and built the first monument but on the quest it still days I have to find the third artifact I really need to complete this quest so I can get onto the next one which is the baby to toddler one so can anyone help me?