Hi Pat,
As I say, not all apartments are the same, some that "look" the same can be 3 or 4 SqrM bigger. The way to do it is to look at the quotas in the deeds. Two apartments, with the same quotas in the same block will pay the same. You don't say if the ones you are comparing yours against are in the same block or not?
If you look in the Jardines, the apartments ( which are all pretty much the same size, but not quite ) vary by up to €21 a month, it all depends on the size of the garden, the number of apartments etc etc and it is the same on La Isla. Each block is a seperate level 3 community that divides La Isla into a number is sections. So depending on the size of the section and the number of apartments in the block and the combined size of all those apartments the fees will vary.
So, as I say, the only real way to understand the differences in the fees is to see the quotas.
Phil