Karbonn K446
Phone doesnt recognise Memory Card

I have K446 Karbon Mobile, I am experiencing the following problems since I bought. I have given once to the service center in Hosur, But No Improvements.

Phone doesn’t recognize the Flash Memory – very often (Though the Memory card is in the slot, it doesn’t list the memory card), By remove and put it back Memory card available for Use, again vanish back after some time

Phone re-boots whenever signal / network searching on it own

Very Low volume on the Ring tones