C# .Net Coder Needed for SMS APP

I have my desktop sms app intergated with plivo and everything is working good.

I only want add OPTOUT feature to my app.

How to process opt outs:

I have a php file on my server that when somebody replies stop it gets added to a database then on the bot before sending a message to the current target number I query that database to make sure the number is not present if is then skip if not then send.

Plivo sends a get request to the url with parameters from=
to=
text=
if text = Stop
add from to database

that is for the php portion then on the bot your should be able to do a get request to an url
with parameter number= the response should say if is present true
if not present false then the bot should do an if variable = true then skip else send sms.