Building permit not granted - Channel overloaded

Hello dear community,
We have been planning our house for a year now and suddenly we are being told that we will not get a building permit.

The construction is planned in a fully developed building area from around 1930.
The construction is planned in the second row because the plots here are very large and long.
The property belonged to my parents and has already been notarized and transferred to me.
Similar constructions have been done several times on this street.
We have been in contact with the city several times and were repeatedly assured that it is possible to build like this.

Now on Friday I spoke to the civil engineering office and was informed that the building application will not be approved because the sewer is already overloaded...
A measurement was recently carried out and the conclusion was made that no new houses can be connected anymore.
Three weeks ago, the civil engineering office told us that we must allow the rainwater to seep away on our property and not into the sewer because there are recurring backflows during heavy rain.
That wouldn’t be a problem, we have already assured them that we will install a cistern etc. Now suddenly they say we are not allowed to connect at all.

In fact, houses are currently being built on the street exactly as we plan to do and one was connected to the sewer a maximum of 4 weeks ago.
Even my architect has never heard of anything like this.
Have you perhaps heard of something similar and can tell me what the legal situation is?
Isn’t the city obliged to ensure that an existing, ready-to-build empty plot can also be connected?

Recently there was even a big report in our newspaper that the city wishes the owners would divide and sell the large plots so that more construction and densification can take place.
Then we do exactly that and it is refused...

Of course, no one expects something like this. We have already signed contracts with the prefabricated house builder and others, cleared the plot, etc. We even had to sell part of the end of the plot to the city if we want to build in the back because possibly in a few years a street is planned to be built at the rear.
Accordingly, we are now stuck with a lot of costs and penalties.

Do you have any advice for us?
Thank you very much!

That would be no problem, here we have already insured, a cistern etc.

Not cistern but soakaway pit is the correct term.

Not a cistern but a soakaway pit is the correct term.

Yes, a cistern in connection with a soakaway pit. That is clear. But that is not the problem either.

What kind of channel is it? Only rainwater or also wastewater?
Is there a B plan? Building notification or a building application?

We were in a similar situation. We also built in the second row and even had to have the B plan changed for it (at our own expense, then applicable to the entire street). In this context, the mayor (small village) beforehand checked whether the individual supply lines for the future houses would be sufficient. But we too were required to let rainwater seep away or collect it.

What kind of canal is it? Only rainwater or also wastewater? Is there a B plan? Building notification or a building application after all? We were in a similar situation. We also built in the second row and even had to have the B plan changed for that (at our own expense, then it applied to the entire street). In that context, the mayor (small village) previously checked whether the individual supply lines for the future houses were sufficient. But we also received the requirement to allow rainwater to infiltrate or collect it.

Building application. It is actually a combined sewer. In the already developed houses, both run into the canal. We were originally told that we were only allowed to discharge wastewater into the canal. Rainwater must remain on the property. And now they say we are not allowed to connect anything at all and therefore the application cannot be approved.

I would bring the topic to the municipal council. If the city wants densification, the civil engineering office must also create the possibilities for it.