Dum Question From A Medicare Newby

[Jon]

I'll be 65 on November first and live on the big island of Hawaii near Hilo. Been here for seven years now, and have been covered by Kauswr Permanete. Was diagnosed with pristate cancer in March of 2017, and have been happy with Kaiser. So, I sigbrd up with Kaiser's Advantage Plus, and added hearing and dental too. My monthly payments will be $250. I thought that was it. Then I got a letter from Social Security/Medicare saying they will be taking out another $134 a month from my Socual Security. I may be a dummy, but I paid into Medicare for over 40 years. I will be paying Kaiser $250 a month for my Medicare coverage. So, what is the $134 for?