parnets visa help

My parents have applied their visa for three times in Guanzhou consulate last year. At the last time, the officer told them they can only re apply after one year. Now, we want to ask them to try again. I wonder how we can help them get the visa. Last three times, they were rejetced without any obvious reason, for the third time, we invited them for my graduation ceremony, the officer said they should apply with other reason, I really can not find other better reason than attending my graduation ceremony. My son i s in China and I want them get the visa and take my little one back. Any suggestion will be appreciated. Thanks in advance.