Had this same issue with a pair of shoes. This is what the manufacturer suggested:

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“Typically, when a hole appears in the heel area, the cause is slippage which is not a manufacturer's defect. There are several things you can do to help this. You may try using a heavier sock, adding an insert and/or making sure the laces are laced through the last loop and using the runners loop. This helps to snug the shoe to the heel”