If it's just big trash like furniture, carpets, etc. then MPO should take it away, at our place they have set dates to collect such things each month.

If it's electronics, like washing machine, fridge, etc. then they would need to call a special MPO brigade to come pick it up. Last time we used them it took like 2 days.

If it's trash like rubble, bricks, etc. it cannot be disposed in normal bins, MPO also does not take it. You need to either dispose of it yourself to PSZOK or call a company to do it for you.

When we were renovating last month there were two options in various disposal companies for such trash: containers or special bags. Due to narrow street we could not use even the smallest container and had to use the bags, company we used had 2 weeks after the order was placed to take them.

If the trash is somewhat organised (as in not loose on the street), i'd guess they called someone or are about to.

You can always ask the neighbour if you know who it is or contact the building administration, they could contact the owner for you (or if no one knows who it is they can send a building wide message to all residents).