I'll try to explain step by step :
1 ) enter this web address : odeme.muski.gov.tr
2 ) click "Normal Borçlar"
3 ) select "Abone No ile" and click "Devam Et" .
4 ) from the pull down menu titled "Bölge" select your area. ( I select "Ölüdeniz" e.g. ) and enter your subscription
number ( Abone No - that you'll find on one of your old bills ) and click "Ara".
5 ) If you see "Borç Kaydı Bulunamadı" in red , you have no unpaid bills.
If you want to see your paid bills , then select "Tahsilat Görüntüleme" instead of "Normal Borçlar" ( Step 2 ) and continue the same way.
The site sometimes responds slow , so try again , it work.
Good luck.