Did you give them a list of your IPs?
Yes, we did. We sent private message with IP list to
piuk 2 weeks ago.
Yes, 176.9.135.190 it is in list of our ip addresses
But I had a look at the blocks listed on your site that were found by 50btc and those same blocks on blockchain.info are showing as relayed by 5.9.24.81. I don't know why that is but it certainly points towards 50btc blocks are being relayed by that IP and not the ones where your pool server runs.
See,
https://blockchain.info/block-height/191015 for eg. how blockchain is seeing 50btc blocks.