Costs for work planning are reasonable

Nevertheless: a mere relocation of a wall should, if at all – depending on the stage you are in – cause a new plan and the associated costs.
Otherwise, you would need just as many stones and as much time anyway, so the additional cost is not understandable to me.

Well, if he offered it including finishing etc., and there was carpet in the children's room but 80x80 tiles + sealing etc. in the bathroom are included, then an additional charge besides the replanning might be justified... but this here is really "from and to" :O

50% upon order placement. Nothing done and wanting money.

It goes on: 90%, and there is still no roof, no windows, plaster, screed, installation .... hands off!

Well, if he offered including removal etc. and there was carpet in the children's room but 80x80 tiles + waterproofing etc. are included in the bathroom, an additional surcharge in addition to the replanning may well be justified... but this here is really "quality and origin" :O

I assumed the shell construction... but more information from the OP is missing for that, yes.

The prices are a dream (for the entrepreneur)! Take a wall: A mason builds it in 0.5 days (costs 4 hrs x 45 EUR). Plus 100 EUR material and 15% surcharge. That makes 322 EUR (values calculated generously). Round up to 400. Where do the 1300 come from then? I have a very, very bad feeling!

Awesome payment plan

Which bank would even go along with that?

It goes on: 90%, there is still no roof, no windows, plaster, screed, installation .... hands off!

I already saw it but it doesn’t matter anymore.

A bank should not care