Renaming picture while saving base64ToGallery

My code below, can’t be simpler than that:

this.base64ToGallery.base64ToGallery(this.imgurl, { prefix: 'testpicture, mediaScanner: true }).then(
res => {

When picture is saved, it is saved as testpicture201982482856.jpg.
First problem: i dont know why but it is saved as month old 2019 ‘8’ 24 ( phone is set all ok, current date 14.9.2019 )
Second problem: is it possible to save it just with prefix without that generic date?