Currently I own a lot of altcoin, I bought them at ico. My account is being downgraded several times. There are many people who say bitcoin will continue to decrease, so altcoin prices also decreased compared to USDT. So now, should I sell them and wait for the price to buy back? Give me advice 
I would like to suggest that you must hold your altcoins until the prices of crypto in the maket increased because it is just takes time for the prices to increase. Be patient to gain your profit which is worth holding. Bitcoin will increased in couple months or years for sure. My advice is to buy when its low and to sell when its high.