Having already replaced all before, to no avail, must I use brand engine coils?

What is your question?

I have been driving my 2000 Inf I30 with the engine light on for the last 10,000 miles. Less than 1yr ago I changed the en. coils to a generic brand coil, mechanic said it would be fine. now the problems are returning and now Im being told that the coils being bad killed the cat converter and it needs to be changed to. so this is a 2 part Q" 1. do I need to re-replace the engine coils with Genuine Nissan coils> and 2. do I have to replace a cat converter ($600.) or use the "Liquid Solution cleaner" ($200.)? Please advise, Sincerely thanks ZkingD