As indicated, just becasue your grandma files a complaint doesn't make it true. You only have to do what is in the court order. Everything else is noise. If the order does not require you to make the kids answer the phone or respond to e-mails you cannot be held iin contempt. Nothing you have stated make believe a valid case against you exists.
You can request a modification or termination of visitation. Delaware does provide the right for a grandparent to visit. The Court is obligated to use the "best interest of the child
" standard. The burden is on the grandparent to show that visitation with him or her is in the child's best interest.
In deciding whether to award grandparental visitation rights, the Court will considers such things as:
The wishes of the child's parents;
The wishes of the child; and
The nature of any prior relationship with the grandparent.
Given what you have described you could potentially get visitation revoked.
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Please be aware that my answer is not legal advice, it is merely information and no attorney client relationship has been formed. You should always contact a local attorney for legal advice.