If you provide how you extracted your RNA I may be able to comment. It reflects on impurities (see: https://dna.uga.edu/wp-content/uploads/sites/51/2019/02/Note-on-the-260_280-and-260_230-Ratios.pdf ). You may perform a NaOAc purification to improve
If the concentration is too low, then the quality will also appear to be low, even if it isn't. The RNA needs to be at least 20ng/ul and it's best to use at least 1.8ul.
It's usually best to try a few housekeepers to see which one works best in your system. What are the possbile causes of RNA conamination in your procedure?
Which housekeeping gene should I use? Because I tried with 18S, and in my experiment the CT value for 18S goes in the range of 12-15. So, I could not analyze the data.