You have what's known as a SMETS1 meter, provided by Secure Meters. They will only work with suppliers that have an arrangement with Secure which PP do not as they do not install SMETS1 meters. As Angela has mentioned they are currently trialling SMETS2 meters and could replace your 1st generation once they are ready to continue with the rollout.
One thing that you may be interested to know is that the next phase of the smart rollout will involve the enrolment of SMETS1 meters into the central network so that they operate in the same way as SMETS2, meaning any supplier can operate them. This process, for Secure meters, is due to start later this year. If you're still with PP at that point they won't need to replace your meter and it will become smart again.