Legal Malpractice

[LWBneed2no]

What is the name of your state? Indiana. I have a 19 year old son in college and was paying his mother $5.2K in child support even though he'd been living in another state attending school full time and making over $20K a year for almost 2 years. I was also paying 50% of his college and medical expenses. I consulted an attorney about whether I could get the child support ended and have my son contribute to his own support and the attorney said it would not be a problem. Once I paid him the initial $500 he made several errors.
1. My ex filed a contempt of court charge based on medical and tuition costs from the previous year last October and he never told me about it. I found out in April in court.
2. He made an offer to my ex wife's attorney to leave things as they were without consulting me
3.He neglected to tell me that, under Indiana law, if the divorce decree did not mention college my support would end AUTOMATICALLY when he turned 21 (13 months from tomorrow). Rather than counsel me to not take this to court, he instead said I'd be better off. The decision that came down raised my support from $100/Week to my ex to $187/Week to my son PLUS $161/Week to my ex for any time he spends 7 consecutive days under her roof. I now pay 61% of his college and 82% of his non-covered medical expenses FOR AT LEAST TWO MORE YEARS! I also have to pay $250 a month for last year's medical can college expenses. This with me having two children living with me from my current marriage and I bring home less than $39K.
When the decision came down I sought a legal opinion on whether to appeal and only then was I told about the support ending automatically at age 21. Wasn't it malpractice for him not to tell me this fact? Not only was I not told of this point of law, he advised me to proceed with the case. Can I sue him and would I have any chance of winning?