I can't help you with the books at the moment, but perhaps I can give you a few other tipps to get a grasp on your English.
Consider looking for those books in flee markets or second hand shops in Berlin to spare some money, or check out some public libraries (Bibliotek) in town and perhaps borrow them for some time.
Please check out this website for interesting and useful material from the British Counsil https://goo.gl/hIZsqV
You can find here useful help with exercises, podcasts and grammar.
I can link you to some more useful material, please help yourself, I hope it's going to be useful.
An intermidiete pdf book https://goo.gl/PkgDsn
A collection of links to useful material for different learning levels https://goo.gl/IGcVQO
There are also useful apps and websites (free) that could help you out like Babbels or Duolingo. You need to make sure they offer the platform also in your native language or another language you can understand though.
I would suggest to find a tandem partner here in Berlin: some other people lerning your mother tongue that you could help out while learning English from them. Look on facebook, there are groups especially for that. Also some websites provide a database of people that are willing to do that.
You could also participate in some couchsurfing or language exchange events here in berlin. It shouldn't be too difficult finding something through facebook regarding this, but please if you have problems let me know and I'll try to help you with that as well.
I wish you success with your English learning!
Best of Luck,