Hmm, This is odd, Right I know it sounds fishy but i have used my mothers debit card in the past to get some games on here before, but most of the 300+ games i own i brought myself via paypal that my debit card is on.

Anyway as i dont get payed for a while i asked her if i could use her card fot the pick 5 bundle, she said it was fine

But seems like i cant use the card on here anymore, It just says invalid number and the number is right, It's a maestro card i dunno what next :/

Dunno if there was some news about this so please fill me in if there was.

I just used my debit card for it, it should be okay. Try it again in a little while and see if that helps, or if you can, switch web browsers. Make sure to check your bank statements to ensure you aren't double charged.

I bought I Have No Mouth and I Must Scream on the release day with VISA debit card without problems. Have you tried to deal with GOG support?

Most of the time if there's an issue it falls either on the web browser or the website being busy. Generally 3 tries is the point where you start asking support.

I guess it all depends from where is your card..
Here, national debit cards wont work with Paypal.

I haven't been able to buy with my debit card since ages ago (well, a month or two maybe). Apparently they're trying to fix it or something. That's what I remember reading somewhere at least.

My deduction is that if s/he hadn't had any problems paying one way and then couldn't use another type of paying in presumably one browser, the issue might be something related to GOG. Or the staff might know more from their log files.
By the way, my experience is that it was always a server's outage or unsupported card type/provider. I mean in general, not GOG.

Some people, myself included, had problems purchasing games via a Visa Electron card. Five days ago I got a response by a GOG rep that the issue should be fixed, but haven't tried yet as there's nothing that I'd but at the moment.

Well if the current card has yet to make a purchase from gog, it could of been blocked at the bank

Visa Electron problems are gone now - for me at least. If gog's form says number is invalid and you are SURE it is ok than very likely while last update they broke function that calculates integrity of card number. Call gog's support as this 'integrity check' appears before they even contact your bank and process transaction.