This is exactly what happened to the said client. This client created a ticket with a demand to enable withdrawal of MONA for his account, what is absolutely impossible because of the attack on the MONA network and public refusal of the developers to bear responsibility for that. We replied to the client with the explanation regarding MONA asset, but he decided to start spreading false allegations, publicly accusing the Exchange of fraud, and thus misleading the other clients.
This seems highly irregular on how your exchange is handling the 51% attack on MonaCoin over a year ago. I realize that you tried to get the Monacoin developers to compensate your exchange for the loss incurred by double spends/invalidated coinbase coins; however it is abundantly clear that they are not going to compensate anybody. I really do not see how this is the development team's fault, any way. All POW coins are vulnerable to a 51% attack, although some coins have a more robust network of miners, so a 51% attack is not feasible.
I read your term of services, and to handle such situations, you give two possibilities. One was to go after the development team. However, Monacoin was not an ICO and it it did not start out with a premine. Therefore, even if they were responsible, I do not see how they would have the deep pockets required to compensate exchanges/pools/individuals for an act done by a malicious miner. Your second option was to socialize the loss. However, the fact that your exchange continued to allow people to trade this coin probably has made implementing this option a nightmare. I find the fact that your exchange did not disable the trading on this coin when you disabled the wallet highly irregular.
I realize that the 51% attack was not your fault either. However, now you are in a situation where you are holding your client's Monacoins hostage. Your exchange should have disabled trading and socialized the loss, rather than let this mess get even more complicated after a whole year.
Edit:Supporting this flag. Livecoin should have implemented the second remedy, that I have bolded, in a timely manner.
The Service do not bear responsibility for losses incurred by vulnerability or any kind of failure of software (nodes, wallets) used by the third parties, or glitch in the software (nodes, wallets), provided by the third parties, as well as failure of blockchains or any other technical problems specific of Cryptocurrencies traded at the Platform. The Service is not liable for damages due to late report from cryptocurrency developers or representatives (or no report at all) of any issues with cryptocurrency including all sorts of forks, node technical issues or any other issues potentially resulting in fund losses. In this case there are two options of compensation for losses. The priority option - the Service is making all efforts to enforce this option is to induce cryptocurrency developers or representatives to compensate for the losses. The other option is to write-off relevant amounts from the Customers accounts in proportion to their deposited amounts of this particular cryptocurrency at the Platform.