The supplier has incorrect meter numbers in the system - what to do?

Aha, so we are talking about Market Location ID and not about the meter ID. This was introduced for these cascades a few years ago.

They partially also break it down to the total meter, which, during a conversion, used to be the heat pump meter anyway. So it DOES NOT HAVE to be a made-up ID, BUT it CAN be.

I have already spoken to them on the phone. There are Pfalzwerke (supplier) and Pfalzwerke Netz (grid operator). I have spoken to both. The supplier referred me to the grid operator, but the grid operator is not exactly a service star. No resolution is to be expected anytime soon. I would actually have to go through the BNetzA for that.
If anything is wrong at all. Maybe it is the thing with the virtual meter numbers that someone explained earlier.
Currently, I am getting no answer on that. I can't reach an electrician, the grid operator has a customer hotline that initially intercepts all inquiries but has no clue.

Then I would send the grid operator a registered letter and ask for clarification.
If that doesn't help, I would work with the wrong numbers, i.e. conclude a new contract. They are stored with the grid operator and assigned to you.

The network operator can (!) indeed just make up the heat pump meter with the number WP34567, report the value of this meter as (GZ12345 minus HZ23456) to the electricity supplier.

But you should actually be able to find that out through the network operator, right? So they would have to have somewhere documented that wp34567 is indeed gz12345 minus hz23456. With the insights here, I would probably try again with the network operator hotline (or try it in writing) (or ask the electrician again?). They must be able to give that to you in writing (and I would like to have that then). So I would feel uncomfortable with the construct "electricity contract on a meter number that I cannot assign," whether with the basic supplier or not (what if there was simply an error in recording and this is not even your connection? If that is a virtual number for your connection, that’s great, but I would want it confirmed before I do anything with it). And with "just registering on the meter number that is on the meter," I also somehow see problems coming (in the direction that the switch doesn’t work at all because the operator says "I don’t know it" or in the direction that you suddenly pay both). That means for me the priority before switching would be to clarify the meter numbers and, if possible, reduce the installments until then.

Aha, so we are talking about Market Location ID and not about the Meter ID. This was introduced for these cascades a few years ago.

I feel like reading about this just made me smarter again. That seems to be exactly what HeimatBauer describes, right? Google also says something like if you want to know the Malo-ID, either look at the last invoice or ask the grid operator... Edit: But I would have expected it to be named like that on the invoice/registration

Bayernwerk and EON took nearly 2 years to properly record my cascade in their system. Before that, I always had to pay household electricity including heat pump consumption on top (the heat pump consumption alone was of course also calculated).

Dozens of calls, hours in waiting queues, and many unanswered letters and emails later, it finally worked out including a hefty credit.

First, follow up with the grid operator (after checking with the installer) to see what is actually stored in their system and how. In case of doubt, have it adjusted. Once that is clarified, settle it with the electricity provider.

Stay persistent, don’t give up. The prevailing poor service there made all telephone providers suddenly seem like exemplary companies to me. I hope it will go more smoothly for you.