Mercari complaint: False Advertising

This is the third time that these had happened to me at Mercari. I bought items for sale from Mercari sellers (sewing machine, set of 6 stacking chairs. 2 stacking chairs) days then weeks passed, Mercari sellers just stop responding to when the items will ship out as if the sellers just vanished or dropped dead in the middle of the transaction. The 1st time I requested a cancellation for an unresponsive seller got my refund. The 2nd time, the seller cancelled without any explanation not a single response from this seller. The 3rd time the seller asked for more time to ship I did, then another request for more time I did again now the seller just vanished into thin air after almost a month of waiting. I can’t even request a cancellation at Mercari because when I tried to contact Mercari, the item that has not shipped is not showing up in the selection to be able to request a cancellationrefund. I have contacted Mercari about this issues responded that they have no control over their sellers. Mercari untrustworthy sellers are allowed to roam free in their platform without any sort of repercussions for not fulfilling their part as sellers.