I don’t make use of ProBit exchange, I don’t even know the two exchanges you have mentioned here (Mxc and ProBit).

But, have you ever contacted ProBit customer support before? That can help you determine how long it’s going to take them to reply your mail. And by the way you should check the reply you got from a bot they might have stated how long it typically takes them to attend to or reply customer complaints; other exchanges I use, once you send a mail and a bot replies, in the email it will state how long it take for them to reply. Or you can as well check their FAQ. And moreover, some companies, due to Covid-19, has been less active.