What type of auction? The county courthouse? And did someone other than the bank buy it?
You could attempt to contact the bank. If you still have the posted notice, try that number first. If the previous owners are still at the house after it forecloses, usually they will send a sheriff to evict the residents. Has that happened? Or are the previous owners already locked out of the property?
Also....Before the bank foreclosed, they would have posted notices of eviction at the property. If the owners still didn't vacate as instructed, by the time the property is sold, generally the bank will send a sheriff and the bank's representative to have the residents move out, and then they will to remove the items from the house, and put them outside, the garage etc. Then they would have changed the locks. It's rare that a foreclosed home still have stuff in it by the time it is turned over to the new owners