This sounds like there may be a problem with the button contacts on the circuit board inside.
If the warranty is still valid, you should return it to your place of purchase for a refund or exchange.
If the warranty has already expired and you are handy with a screwdriver, then you can try unplugging and disasembling the unit yourself.
Once you get the unit apart, look at the circuit board directly under the button pad. Check for any damage or cracks on the board itself, or if the button contactors in question are broken or displaced. Also check for any signs of corrosion or residue there and clean it off the circuit board with some Isopropyl Alcohol if necessary.
If you find any actual cracks in the circuit board, then the unit is like a total write off since you will be unlikely to find a source for just that part unless you get lucky and find something on EBay. There are complete replacement units currently available on EBay, but nothing for less than $100 besides this one auction item which is currently at $61 US:
Just use your mouse to click on the link, which is the underlined and highlighted text just above. This will open a new web browser page automatically for you and allow you to view the information and items at the website indicated.
Thank you very much and good luck.