What are you complaining about? A notice period of four weeks is better than a notice period of one week!
Irrespective of what the employer may have indicated, the minimum notice period by law would have been one week's notice between one month and less than two years continuous employment, then two weeks' notice for greater than two years continuous service, plus one additional week's notice for each further complete year of continuous employment, up to a maximum of 12 weeks. So if you have been there 5 years, that's 5 weeks minimum notice period. Employers may offer longer notice periods than I have quoted above - these are the legal statutory minimums.
The method of salary payment and its frequency is irrelevant to the notice period.