You can not just go and dig up a grave or even an ashes interment , it is a serious offence. Permission would only be given in very unusual circumstances.
This a family dispute and the church has nothing to do with it.
Someone in the family must have arranged the interment of the ashes and where it was.
There is obviously a family dispute here as you say ''My family didn't tell me my Father had passed away until after the funeral'' This family problem is what you need to sort out , you will not get permission to disturb the ashes . Just concentrate on resolving the family problem.
There was a very similar problem on here a week or so ago , where a daughter did not want her name used on her dads grave stone. The answer was the same. It is a family matter and nothing to do with the church which has just done what it had to do in suppling the grave plot at the request of the person who organised the funeral and paid for it.
It is quite normal that an ashes interment is marked only by a stone and that all these stones are identical apart from the name.