Need help with my billboard shader

Hey, I am working on a billboard shader which I am using for my 2D sprite based old school doom like shooter. The billboard shader I created(mostly part copied from google) is working fine but if the object rotates, the sprite is rotating with it. So I want some suggestion how to make the sprite not rotate with the object, so it will always face the camera. Sorry if anything I said don't make sense as I am really new to shader programming. Here is the code I am using for billboard.

 Shader "Billboard"
 {
     Properties
     {
         _MainTex("Texture", 2D) = "white" {}
         _Color("Color", Color) = (1,1,1,1)
     }
     SubShader
     {
         Tags { "RenderType" = "Transparent" "Queue" = "Transparent+500" }
         LOD 100

     Pass
     {
             ZTest Off
             //Cull Off
             Blend SrcAlpha OneMinusSrcAlpha

             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma multi_compile_instancing
         // make fog work
         #pragma multi_compile_fog

         #include "UnityCG.cginc"

         struct appdata
         {
             float4 vertex : POSITION;
             float2 uv : TEXCOORD0;
             float4 color : COLOR;
             UNITY_VERTEX_INPUT_INSTANCE_ID
         };

         struct v2f
         {
             float2 uv : TEXCOORD0;
             UNITY_FOG_COORDS(1)
             float4 vertex : SV_POSITION;
             float4 color : COLOR0;
             UNITY_VERTEX_INPUT_INSTANCE_ID 
         };

         sampler2D _MainTex;
         float4 _MainTex_ST;

         UNITY_INSTANCING_BUFFER_START(Props)
         UNITY_DEFINE_INSTANCED_PROP(float4, _Color)
         UNITY_INSTANCING_BUFFER_END(Props)


         v2f vert(appdata v)
         {
             v2f o;

             UNITY_SETUP_INSTANCE_ID(v);
             UNITY_TRANSFER_INSTANCE_ID(v, o); 


             float4 worldOrigin = mul(UNITY_MATRIX_M, float4(0, 0, 0, 1));
             float4 viewOrigin = float4(UnityObjectToViewPos(float3(0, 0, 0)), 1);
             float4 worldPos = mul(UNITY_MATRIX_M, v.vertex);
             float4 viewPos = worldPos - worldOrigin + viewOrigin; 
             float4 clipsPos = mul(UNITY_MATRIX_P, viewPos);
             o.vertex = clipsPos;

             o.uv = TRANSFORM_TEX(v.uv, _MainTex);
             UNITY_TRANSFER_FOG(o,o.vertex);
             return o;
         }

         fixed4 frag(v2f i) : SV_Target
         {
             fixed4 col = UNITY_ACCESS_INSTANCED_PROP(Props, _Color) * tex2D(_MainTex, i.uv);
             UNITY_APPLY_FOG(i.fogCoord, col);
             UNITY_SETUP_INSTANCE_ID(i); 
             return col;
         }
         ENDCG

     }
 }

}