Vodacom - whatsapp message delay.

I only receive whatapp messages when i go into whatapp. If someone send me a message on whatsapp and i dont go in for more than 2hours (duration of time can be more or less) i will only receive the message once i go into the app. Its shows the time the person has send it but it only pops up when i go in. I went to the Vodacom store in Greenstone and they said that it is the app i mist delete and restart. This is a problem that i am struggling with for x3+ years, with x3 different phones. So i do not believe it is the app, it doesnt matter if i am on data or wifi. This is starting to upset the people trying to contact me and they always say that i switch my phone/data or whatever off to not receive message. I hope you can resolves this or I'll have to switch to a different service provider. I remember seeing an advert on route to work saying that the Gautrain is not the only fasting thing and that your 4g network is much fast.... We'll the proof is in the pudding, but im bot having it.