Hi @Ykcivikas, I'm sorry to hear about your phone. 
The price may vary between markets so I'd recommend that you get in touch with your Local support team. They are the experts on your market and they may be able to provide with an estimated cost for repairing the back cover on your Xperia Z3+.
They will also answer any and all questions that you have may have regarding warranty, local service routines and so forth!
Let me know if that helps!
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