The planner does not perform any calculations according to DIN 276

I have been reading diligently here and searching the forum - but I am simply overwhelmed.

We have the following problem. My father bought a listed building 5 years ago - this was accompanied by an architect.
An inventory was made - and remodeling costs of about 400,000 euros were specified.

Unfortunately, there is only one email in which the architect confirms that my father cannot spend more than 400,000 euros and that the costs are definitely within this range.

But this is not the (current) main problem at all. After 4 years in a holiday apartment, the construction - which was supposed to take two years - has now been completed.
Of course, the costs have gone completely out of control - which is why my father addressed the architect several times.
Towards the end of the project, he simply gave up and paid the bills because the house just had to be finished.

Now we have asked the architect to provide us with the cost estimate, calculation, and determination according to DIN 276 so that we can understand the costs and especially the overruns.
This is simply being ignored - to this day no estimate, calculation, or anything similar according to the DIN has been made.
She even said that this standard was not known to her.

She is now presenting her final invoice and claims that she has fulfilled all her obligations.

What simply leaves me speechless. We were not informed about any warranty periods even though defects are already showing and we have asked about them.

In addition, there is still an unresolved invoice with a roofer because he set up scaffolding here for weeks which was not used. (However, I do not consider this to be my father's fault either.)

Do we have to pay all of this and really have no right to a calculation or determination of the costs so that we can understand them? And does my father really have to pay the 10,000 euros for the scaffolding - the planner is actually responsible for scheduling - that is why we hired her?!

I would really be grateful for help - after all the trouble and the construction time we are slowly reaching our limit - and the behavior of the architect cannot be lawful. Is she really allowed to present the final invoice without us having any claim to the above-mentioned services?
It is a completely normal architect contract according to HOAI - she was responsible for LPH 1-9.

Take a look on the homepage of HOAI under the basic services (links are forbidden here). You will already find at service phase 2

Was she really a qualified architect?

Take a look at the homepage of HOAI, under the basic services (Links are prohibited here). You can already find it in service phase 2 Was she really a trained architect?

I have pointed this out to her – multiple times. She says she doesn’t have to fulfill all services, so the service phases are also billed proportionally. She just plays dumb – or takes us for fools and insists she doesn’t have to fulfill them. (She has a diploma from the FH – supposedly a specialist planner?!) When I look into the HOAI, I feel sick about all she hasn’t provided. This would go beyond the scope here.

But I can still demand the calculations (I have already done so multiple times, also citing the HOAI and that this is listed there as a basic service).

I have never heard of an architect guaranteeing the construction sum.

That's not what it's about at all. And I never said that either. She did write an email at the beginning in which Aue confirmed that she was aware that we cannot spend more than 400,000 and that the project could be realized for far less, and she always insisted on this in conversations. But that's it.

And I mainly want to know whether she can really refuse all calculations, estimates, etc. according to DIN, or whether she can claim that she only has to fulfill the services partially.

There is surely an offer from the architect with itemized costs for design, approval, construction management, etc., and presumably there are also offers from the craftsmen that state what is included. If the scaffolding was commissioned independently because it is used by several craftsmen, then it must also be paid for the entire duration.
After 4 years, finding out who did what wrong and when is impossible. The only leverage left is to withhold payment of the architect's final invoice and see what happens next.