Bad Service

About a month ago my 2011 chev spark was taken to Drew mechanic in st Francis Bay to replace clutch plate and cable. After having the car for 3 weeks he informed me that that my car won't start, but when he got the car there was no problem. I then paid a auto electrician to come do a test.... He said fuses are fine but it seems as if the mechanic let 2 positives touch & and has blown the computer box. Drew said he he isn't responsible for anything and that I must pay him R4500 and then I can take my car & get it sorted out somewhere else. Please could you assist me with this matter? 500 I really think that drew is responsible to have my computer box sorted out as when he got my car it started Thank you in advance Lisa