Since this stopped and started on its own, it was likely a global issue with the hosting company (perhaps they were updating the PHP version or they had someone hack into the system and make changes that caused PHP to stop, such as removing the .php extension from the list of file types that are parsed by php.) If your control panel has a setting to enable/disable PHP support for your account, this could have gotten disabled, perhaps due to a corrupt database and/or someone hacked into the system and did this on purpose to disable the web sites...
Another possibility, given the unhelpful answer they gave you, was that someone who thought they knew what they were doing at the hosting company made a change, either deliberately or by accident. A helpful hosting company, even if it is something that is out of their control, should have responded that they would look into the issue, especially when told that PHP pages that were working suddenly started appearing as the actual PHP code (this is a very specific symptom that the PHP parser is not operating.)