Bugged Quest

Hi,

My name is Alessandro Vidussoni. I'm playing swtor on my Alividy on Darth Malagus server. I'm doing a quest "Taris: Bonus series". It bugged at the end and I couldn't turn it in. So I abandoned it and restarted. Now I can't even do the quest because it requires me to do a task that is already completed from the first time I did it.

What do I do?

Best Regards,

Alessandro