OfferUp hasn’t paid me. Take action

Level 1
I haven’t been paid by OfferUp. I received notice that my money was deposited on January 22 - and it wasn’t. $368.40 from a $400 transaction has never been received. To be clear-the buyer paid. It’s OfferUp who is profiting from my money. I contacted OfferUp on their website and they said someone would follow up by email. They never did. I contacted them a second time through their website, and once again, no reply. Then I contacted them through Facebook and received a reply through Messenger saying it had been deposited and to contact my bank. I asked them for a deposit transaction confirmation number and they did not provide one. They just repeated the same info from the original email they sent saying the money was deposited on January 22 and to contact my bank. This was my first experience using OfferUp - and was not a good one.
Level 1
An update - still no resolution from OfferUp   
- sold on Jan 21
- buyer paid on Jan 21
- I shipped on Jan 22
- received by buyer on Jan 25
- notice from OfferUp that payment was deposited on Jan 28
TODAY's DATE 2019.02.26
That's 29 days from the date the deposit was supposed to have been made, not including today.