Angular 6: Service is undefined

I'm using Angular for the first time and I'm trying to get a service running so I can get the contents of the file. I followed to heroes tutorial exactly where they explain how to do it and I did in the exact same way, but for some reason it doesn't work.

I get an error saying ERROR TypeError: "this.fileService is undefined", and I'm not sure what the issue is.

about.component.ts

import { Component, OnInit } from '@angular/core'
import { FileService } from './../file.service'

declare var require:any;
const markdown = require('markdown').markdown;

@Component({
  selector: 'app-about',
  templateUrl: './about.component.html',
  styleUrls: ['./about.component.scss']
})
export class AboutComponent implements OnInit {

  constructor(private fileService:FileService) { }

  ngOnInit() {
    const aboutmeraw = this.fileService.readFile("./../assets/md/aboutme.md");
    this.aboutme = markdown.toHTML(aboutmeraw);
  }

  aboutme:string;

}

file.service.ts

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class FileService {

  constructor(private http:HttpClient) { }

  public readFile(file:string):Observable<any> {
    return this.http.get(file);
  }
}

I know the method I return the HTTP file is wrong, but that's not the error I'm getting.

What's going on and how can I fix it?