What is the ABC product? Is it a registered mark? Is your product similar to or the same as the other product? Is the company also selling on Apple Store? How long have you been selling? How long has the company been selling? Could an ordinary consumer browsing app store be confused by the names?
Without such information it is almost impossible to answer your question. To be safe, just change the name of your product since you mentioned you just began to sell on Apple Store recently. It is likely that you are infringing their trademark rights, regardless whether the mark is registered.
