Build a apk on android whatsapp

I need an Android app To Help me send marketing messages to the contact list in my phone via whatsapp. Issue I have a few thousand contacts whom I need to send updates to. Using Whatsapp's original app, I am restricted to a broadcast limit of 5 contacts each time, not to mention having to select each contact manually. App Specification This app which I require should be able to: 1) read contacts in my contact address book and load/show only those who are also using 2) Allow multiple select and select all function for those contact. 3) A text box to enter message (and if possible to attach files). 4) To send the messages out in batches via whatsapp. (Caveat: The broadcast function cannot be used as some customer don’t keep or key in my number as a contact.) 5) The end product can be standalone application or a web-based interface (open for discussion on implementation). Preference is for apk although as long as my goal is achieved, either is fine. Requirement Please send me a video or screenshots of your proof of work in this field as I had been conned by a very dishonest freelancer who claimed he could do this, took my money and gave me nothing. Payment Please note that I will NOT send any money until I see proof of work. Balance payments will only be released in accordance to this website's rules, ie upon successful completion and satisfaction of product. Do bid only if you can produce and comply with these requirements.