I'm not sure that you are supposed to have the "\n" in your response.
I used this json validator (https://jsonlint.com/) and found that a valid JSON would be
{
"make": "Ford",
"model": "Focus",
"VRM": "AB12CDE",
"VIN": "XXXXXXXXXXXXXXXX"
}
So this should work:
$str=str_replace("\r\n","",$response);
$array_response = json_decode($str, true);
$make = $array_response['make'];
Now you have an array and you can easily access the make like explained