I constantly am getting interrupted sleeping cycles, how to get 8 hours?

Sleep hygiene. To reset your sleep clock, go to bed at the same time every night, awaken at the same time every morning, don't nap during the day, use the bed for sleeping (not eating, TV watching, reading, etc), if you awaken during the night, stay in bed until your determined awakening time.
You or environment. Find out whether it is you or the environment that is causing the interrupted sleep. If it is you, best to consult a physician to seek proper diagnosis. Interrupted sleep can be caused by various medical / psychiatric disorders. Ignoring it will delay finding something that is potentially easily treatable and prolong suffering. One example is sleep apnea.