My sony cfs-w360boombox plays tape at high speed
there may be 2 possibles
1, the pinch roller is not going down and staying in the fixed when during playback, easy way to check power down the unit, press play and see if it looks firm, it will push back, if working right
if its loose, it may well have come off a little sping, and may well be an easy ish fix, by someone who know about cassette decks,
2, the speed adjustment has failed, there will be an internal speed control, which keeps the playback at a correct speed, if this has failed it may be fixable, but only by someone who can take it to bits and remove and solder a new one in, and they are very small and Sony items i have had have failed on speed control! too for me its a junker box
good luck