在1and1共享主机托管的joomla中自动更改文件权限

I manage a Joomla website hosted on 1and1 shared host. Recently, I found that an important file keeps automatically changing its permission and even if I change it back, after 15 seconds or some, it will be changed back somehow.

Does anyone know whether it's a Joomla problem or a 1and1 problem?

Note: I know there are some PHP functions that can change file permissions.

It was the Administrators' action. He want to warn me that I have to pay them.