Angular 18 computed not a function

I'm using Angular 18 with signals. My CalculationService basically calculates a price based on some parameters. Building with ng serve doesn't throw any errors neither does VSCode, however my browser throws the following:

 ERROR TypeError: this.doorAmount is not a function at Object.calculatePricePerDoor [as computation] (calculation.service.ts:52:48)

And my component doesn't load.

calculation.service.ts

import { computed, Injectable, signal } from '@angular/core';
import {
  basePrice,
  basePricePerDay,
  basePricePerDoor,
  minutesPerDoor,
  stepPrice,
} from '../consts';

@Injectable({
  providedIn: 'root',
})
export class CalculationService {
  #price = signal(0);
  #basicDoorAmount = signal(0);
  #electroDoorAmount = signal(0);
  #automaticDoorAmount = signal(0);

  doorAmount = computed(this.countDoorAmount);
  price = computed(this.#price);
  pricePerDoor = computed(this.calculatePricePerDoor);
  priceStep = computed(this.calculatePriceStep);
  hours = computed(this.countHours);
  days = computed(this.countDays);

  constructor() {
    this.calculatePrice();
  }

  calculatePrice() {
    this.#price.set(
      basePrice +
        this.pricePerDoor() +
        basePricePerDay * this.days() +
        this.priceStep()
    );
  }

  setBasic(amount: number) {
    this.#basicDoorAmount.set(amount);
  }

  setElectro(amount: number) {
    this.#electroDoorAmount.set(amount);
  }

  setAutomatic(amount: number) {
    this.#automaticDoorAmount.set(amount);
  }

  private calculatePricePerDoor() {
    const { basic, electro, automatic } = this.doorAmount();
    return (
      basic * basePricePerDoor.basic +
      electro * basePricePerDoor.electro +
      automatic * basePricePerDoor.automatic
    );
  }

  private calculatePriceStep() {
    const { basic } = this.doorAmount();
    if (basic < 21) return 0;
    if (basic < 101) return stepPrice[100];
    if (basic < 251) return stepPrice[250];
    if (basic < 1001) return stepPrice[1000];
    return stepPrice[1001];
  }

  private countDoorAmount() {
    return {
      basic: this.#basicDoorAmount(),
      electro: this.#electroDoorAmount(),
      automatic: this.#automaticDoorAmount(),
    };
  }

  private countHours() {
    const { basic, electro, automatic } = this.doorAmount();
    return (
      (basic * minutesPerDoor.basic +
        electro * minutesPerDoor.electro +
        automatic * minutesPerDoor.automatic) /
      60
    );
  }

  private countDays() {
    return Math.ceil(this.countHours() / 7.5);
  }
}