Christians, whether of the one or other denomination, are, or should be, taught that attempting to contact the dead, or tell fortunes is wrong.
The thinking behind this prohibition is, I believe, due to the doctrine of God being almighty - if he wanted us to receive messages from friends and relatives who are no longer in this world, he would presumablly have devised more reliable methods than the kind of mediums who are making a living conveying these sorts of ten-a-penny messages.
Here too, we should stop to consider that right back to the days of Christ's apostles, Christians have believed that the gifts of the Holy Spirit should be given freely and that the human mediator should not accept payment.
Obviously, we all know that at times this precept has been ignored, but it has never been rescinded.
Another good reason for the various churches holding to the principle that one should not seek to receive messages from the afterlife is the fact that you have yourself experienced, Sarnia, they are often distressing to the recipient.
There may be such things as genuine premonitions, or genuine mediums. but if so, no-one has yet proved that either do exist.
Another very relevant fact is that, if you google your name and address ,you will, unless you have taken very great precautions against this very thing, which most of us have not, find a great deal of information about yourself and your family online.
Mediums and fortune-tellers are very well aware of this fact, and believe me, they do use the Internet to gather information.
Please, try not to let this incident worry you. Remember your grandfather as he was. If any of our dear loved ones are aware in heaven, or wherever else they are , of what goes on with us on earth, he may well be annoyed that someone tried to make money out of making up such a message from him!
The gentle, loving grandfather you remember would not want you to worry about this.