Transform shapefile to WGS:84 (EPSG: 4326) in Qgis

I am struggeling with an enoying problem here. I received several shapefiles from an colleague that he told me is in WGS:84. If I look at the metadata in Qgis it tells me the following:

In layer spatial reference system units
xMin,yMin 3572722.82,5453423.31 : xMax,yMax 3582448.25,5462926.22
Layer Spatial Reference System
+proj=longlat +datum=WGS84 +no_defs

Now when I try to save it in another projection say WGS:84 Pseudo Mercator (EPSG: 3857) it gives me the following:

 Export to vector file failed.
    Error: Failed to transform a point while drawing a feature with ID '1'. Writing stopped. (Exception: forward transform of
    (62425.896446, 95242.109906)
    PROJ.4: +proj=longlat +datum=WGS84 +no_defs +to +proj=merc +a=6378137 +b=6378137 +lat_ts=0.0 +lon_0=0.0 +x_0=0.0 +y_0=0 +k=1.0 +units=m +nadgrids=@null +wktext  +no_defs
    Error: latitude or longitude exceeded limits)

A similar message is returned in R with the rgdal package. I suspect that the initial projection is somehow wrong. Is it truly WGS84? I would appreciate any help and suggestion to export the file to EPSG:3857. The problem occures with all shapefiles.