I think this formula is very hit or miss for some people. when doing it at a salon there is a higher risk of permanent effects because the stylist most likely follows the application to a T. which means using 450 degrees temperature to seal(which is unnecessary imo) and doing several passes.
are your roots brittle as well? it sounds like an awful expereince!I see that many report the hair being fine after the first application but the problems are noticed about a month or two after. this is why i like to try things that someone else has used more than once with 1-3 months rest inbetween. that way you can really tell how it affected their hair.
Unfortunately you will just have to grow it out but maybe someone will benefit from your experience.