I mined around 4000 charnacoin with the pool
charnacoin.com. The pool shows that coins are paid but I haven't received them on my GUI wallet. The wallet is already synced. What shall I do?

Same problem here. Pool paid out, but wallet is synced, and no money ever showed up in it.
my wallet log:
2017-10-10 04:41:57.703 1896 INFO global contrib/epee/src/mlog.cpp:145 New log categories: *:WARNING,net:FATAL,net.p2p:FATAL,net.cn:FATAL,global:INFO,verify:FATAL,stacktrace:INFO
Height: 25601/168134 (15.2%) on mainnet, not mining, net hash 802 H/s, v1, up to date, 1(out)+8(in) connections, uptime 0d 5h 1m 43s
Wallet not sync yet.
or maybe problem with blocks. try to rescan blockchain. rescan_bc command