Question about final weeks pay after notice period

I need some advice on my final payslip. I recently gave my 4-week notice at work, but my boss asked me to finish up after three weeks. I was under the understanding that I would still be paid for the full four weeks, even though I didn’t work the last week.

I just checked my payslip, and it seems like I haven’t been paid for the fourth week. Has anyone else experienced this? Should I be paid for the full notice period even if I didn’t work the final week? What should I do next?