Toliet Drain Flies

We have been experiencing drain flies for couple months. Had plumber come and he took toliet off and stated we had drain flies coming from toliet pipe. He cleaned pipe out. We also had an exterminator come and spray area. Week later now, and the drain flies are back. Called plumber again who came back. He now stated that the floor underneath our cermaic tile floor around the toliet is rotted out and this is causing the drain flies to still appear. He stated we have two options. One take up new ceramic tile and put in new sub floor and retile again. Or, take toliet back off and but a porcein base which would sit on ceramic floor and then place the toliet over the basin. We have spent alot of money on plumer and exterminator. Help please; is this plumber just giving us good information. thank you

If the sub floor is rotted, that means there is or was a leak for an extended period of time. Does it really seem wise to you to just put a cover over a rotten floor? I think in your heart you know what really has to be done. The floor has to be taken out as much as necessary to get rid of the rotted floor and the floor redone. Perhaps the tile can be salvaged and reused.