Best way to approach going forward?

Uncharted2

I have been a customer service agent for 6 months now. My role consists of customer interaction via inbound and outbound calls, whilst working on behalf of the company's number of clients. My manager has received numerous complaints from some of the services on mistakes I have made on interactions on logging information and so forth. I was made feel like I was worthless and when I asked what services I needed to work on I made feel like it was all services. I have not been in this position before, I feel I did not stand up for myself and that has annoyed me the most. I don't know what to do going forward I don't feel confident in this role any longer. I have always been good at my positions in the past and worked hard all throughout my career history. Any advise is most welcome. Has anyone been in this position before?