Screen Sensibility aftersale - they said screen damages and send bill

pili

Hello

I'm french (excuse my english) and it's my first chinese phone import. certainly the last;

I buy UMI touch pre-sell on geekbuying site.
I paid at the end of february, received it at the end of april.

I used it 4 weeks, i think screen tactile whas not enough sensible, i hope some rom update could resolve that problems.
When i begin to have some problems during calls (sometimes i heard nothing, sometimes we dont hear me..), i decide to use 1 year warranty to repair the problem.
So i mail geekbuying and return my phone to them (return cost paid by me, half refund by geekbuying).

Yesterday they send me news of my phone, they says screen is damaged (it's not my fault, he's working when i send it) and need to be changed, and they send me 47$ fee.
I thought, like in france, warranty means free repair for malfunction. he didn't fall, was not broken, always protect with screen protector 9h and original hard back case.

I won't pay 50 $ for changing screen, because for me it's warranty to take care.
it won't solve reaphone and microphone problem, and i'm not sure it solve the sensibility pb.

I paid 160$ for phone and accessories (140 phone, 10 back case, 10 scree protector), 25$ of return cost (geeknuying refund me only half) and now they ask me 47$.
I have no phone.
I'm really disapointed and will no more buy chinese phone import.
I'm feel robbed.

If someone can help.