Galaxy s4 mini (GT I9192) - Android 4.4.2 .... Storage space depleting even though data being deleted

So this is a recent development since last night.. when the phone suddenly started misbehaving. Hanging, apps crashing, working really slow, screen going blank, Vol / Power key buttons not working etc. Messages kept popping up that storage space is low.. with great difficulty managed to delete apps and other data. Images, audio, video etc. The instant I clear up and check storage it will indicate the appropriate amount - 200 mb, 300 mb... However in a few seconds, the same issues of hanging reoccur, and upon checking storage I see that it has gone back down to 180 mb, 700 kb n finally now its showing 56 kb despite having removed more than 2 gb worth of data and apps. CACHE continually being deleted, best I can do since the phone is barely functioning, but it keeps filling up to about 1.84 mb (not that it matters). Help! I cannot purchase a new phone as I do NOT have the funds for it. I also get a pop up which goes something like android.acore stopped functioning. Sometimes "process system" stopped functioning along with the usual pop ups of Whatsapp, Google apps, Touchwiz not functioning.