Hello
I had the same problem this year my DLA was due for renewal and a form came out and I filled it in and sent it back then 2 months later I got the new PIP form sent to me, I phoned the DWP and they had no trace of my DLA form, I explained that I had filled it in and sent it back, she just didn't believe me and said that I had to fill in the PIP form, which is more or less the same for as the old DLA one. I was s mad not only do I know I filled the form in I even sent it back to them recorded delivery, they seem to have messed up an are sending out both the old applications and the new. Lucky for me I kept a photocopy of my DLA for so I could use it to fill in the PIP form.
They really need to sort themselves out , don't be surprised if you to get a PIP form in the post
Love sharon