I think that to give you useful advice a bit more information about the situation in question is needed.
I can't offer suggestions for how you can act, but as for your mind, just remember that things are only bad because we perceive them to be. Everyone thinks that they are being the best person they can be. Maybe try to understand the person who is bullying you, see where they are coming from, and what might have caused them to act this way. If they are trying to cause you grief, the grief is only as great as you let it be, but their karma will be proportional to their deeds. Imagine taking in their suffering on yourself, and sending them love and compassion, and it will feel like the burden you carry is suddenly much lighter.
Also, just consider how much worse it could be. You could be living in a country without enough food and water. The person could be smashing your windows and beating you, not just bullying you online. Sometimes if we look at our position relative to the other possibilities, we realise that there is nothing to fear, and that our position might actually be something that many people in the world admire greatly. You've come to find the Buddha's teachings, you've also managed to set up your own business, you have great karma and great success, and whatever hardships occur will only be temporary. Just stay calm and honest, thinking twice about all of your responses to this person, only acting in a way that you won't regret and which won't make you worry more after, and if possible, just ignoring the person's actions altogether, and you may then find that it may just pass in no time at all.
Moreover, meditation of all sorts might help with your anxiety and depression. Try giving it a go. Mindfulness is fine, but you might find your mind becomes much lighter with loving kindness meditation. Then you may also develop the ability to not allow yourself to view anyone as bullying you -- because in reality they're only bullying themselves.
May you be well, happy, and peaceful, and may your business flourish and do well. May everything go perfectly for you.