I have stop playing this game for few years. I started playing on ipad and have purchase many packs. i started to play today, but realised that most of my collection are missing . cant even locate any of my legendary cards…Please advise me. Thank you.
my condolences 
Sorry man, i was in the need of some dust.
Check to see if you logged on to the correct account.
Check to see if you logged on to the correct region.
Dig in your memory. Are you sure you never disenchanted those cards? Are you sure you never accidentally or on purpose shared your password with anyone?
After all those steps, if still needed, open a ticket with customer support.
In the Collection, there should be a button labeled “Filters.” Once the filters pop up, by default the “Standard Cards” filter should be active. Click on “All Cards” instead, and see if that helps.
If it doesn’t, you should check to make sure you’re logged in with the correct account and in the correct region, as BigHugger said.
Last time that happened to me, I realised I was logged into the wrong account. Did you have multiple accounts?
They might have gone wild