Best Internet provider (Frankfurt)

Dear Expats!

I'd like to take your advice on the Flat Internet provider. Currently I have O2 but I can't say I am especially happy with them. The Internet is good, but it took them 3 weeks to come install everything and now it takes them weeks to respond to an e-mail, I have to wait forever to reach them by phone (not to mention they charge for every call). I have cancelled my E35/per month Internet with them and they offered me a discount in case I stay. It should be E25, which is ok, but their customer support is still a mess. I wonder if there is anything better on the market and would very much appreciate your recommendations! :)

Yaroslava