First prepayment, now partial payment demanded - confused!

The answers are hair-raising and will bring the OP into big trouble if he follows your suggestions ....

I would seek the conversation...

I actually find all the answers hair-raising except mine. In particular, I wouldn't immediately run to a lawyer.

I would try to have a conversation...

I somehow doubt that the electrician is willing to have a constructive conversation when he quickly involves the collection agency without kindly asking what is causing the delay.

I agree with that. I will first draft a letter and ask what the advance payment refers to and point out the written agreement made.

At the same time, I will list what is still missing and which things are defective.

Interestingly, his offer contains the text "Bei 50% Vorkasse x Prozent Skonto" - we took that. There are no other agreements. To me, the matter is therefore clear. He should first complete the rest of the service, then he will get the other 50%. If a collection letter arrives, I will write to him again and demand that the claim be deferred until the service is rendered. If he doesn’t do that, he will get a letter from the lawyer.

I somehow doubt that the electrician is willing to have a constructive conversation when he comes along so quickly with the collection agency without first kindly inquiring about the reason for the delay.

Yes, correct. When I called the first time and asked why the advance payment, he yelled into the receiver... I told him that if he delivers the service, he will get his money. That’s why the construction site here was at a standstill for 2 weeks, because he simply didn’t show up and continue. We moved in without a doorbell and have a few other things that don’t fit... and then he threatens with debt collection and even sends the reminder to the old address, fully aware that we have moved... one could now suspect intent...

Regarding the invoice: 50% was down payment, now he wants another 30% converted – leaving 20% remaining