brother i understand the situation you are in,i have been through a milder version of that,though alhamdulillah its over now,but i can still feel how horrible it must be for you.
This is the only thing I have thought about for days. first it was telling me to call god names Now it is telling me join partners with god when I pray so I can't even pray
thats exactly what happened to me as well,people might think its like normal waswasa that shaytan puts in your head,but unless one oneself experiences it,one cant be aware of the its strength.its like some ones constantly directing you,arguing with you and telling you to call God names,and associate parteners with Him,its very dominating and you feel so overwhelmed that you cant resist that,it would present a thousand arguments with a huge frequency,you feel you cant counter what its saying(you dont have so strong arguments),and you cant even turn a deaf year to it.it seems impossible to put it off your head,and the feeling that its going to make you lose your faith,eats you from inside.
may be its a test from Allah,but i remember that nothing seems to work.i would recite lahawla wala quwwata illa billahil aliyyil azeem all the time.and i remained peaceful while i was doing that,but you wait a second(during which you dont recite that) to have a breath and it is back...
that was a very precarious situation really...it subsided with time, i got over it eventually.
i did not hear the voices though,but the evil thoughts that came into my mind were so strong imaginations that,normally,they would sound closer to reality rather than imagination,it felt like i could even hear
the thoughts coming into my mind.
i did not have nightmares though,(well,all of the life seemed a nightmare anyway),there was a haziness surrounding me that made me feel i am cut off from the world.and sleeping was the only escape to put such feelings out of my mind.i would cry all the time.i could not explain to anyone what was happening to me.it didnt matter though,cuz people dont understand such things if you tell them,unless they themselves have experienced it some time in their lives.
i have also
lost all my feelings and I feel like I'am dead inside and no how hard I try all I can think about is evil...
that happened to me as well bro...
i dont know how exactly did i get out of this.it just got better all by itself.i kept praying,and reciting the duas that protect you from shaytan.you do recite the quran and those duas please.may Allah help you out,i will pray for you inshallah.i know what a horrible situation you are in.
I don't think praying will get rid of voices, unless you are good at self-hypnosis.
prayer does help...it all depends on how strong is your belief in Allah.He does respond to your prayers.though the effect may not necessarily be instantaneous,it may take some time,but prayer does help even in this case(i know it from experience.)
so bro keep praying,reciting quran and duas.i dont know if my post was of any help to you cuz it mainly consisted of a story rather than serious advice.but i am posting this just because i thought it may be of some help to you,though little,but at least it can make you feel you are not alone,there is someone who understands your situation and it can give you some hope that its possible to get rid of it,soon inshallah.
p.s.i do recommend you to see a psychiatrist.he may give you some medicine to relax yourself and can give you some good advice.do consult some religious scholar as well.if you can find one.
all the best