Blacklisting my phone

I do not understand how can my cellphone be blacklisted and I am not even made aware of that. For months I have been calling customer services complaining about my phone not having network and not being to use some services on my phone. I was transferred from one department to the next being told different stories by agents. Now last week for the very first time I spoke to someone who told me that my phone was blacklisted six months ago. I signed and emailed back the unblacklisting form and still got another email saying that I must email someone else!!! Like what must I do!! I do not understand why no one is willing to help me because I have all the necessary details, but no I am being sent back and forth!!!!!!!