Very very slow mobile internet

Hi,

I’ve been using O2 pre-paid for a year now and it’s been fine so far except for the past 2 weeks. My mobile internet is super slow to the point that I can’t use any internet at all, in wherever I go all over Berlin as I commute around a lot. Nothing loads, even apps like instagram, google maps, youtube or even the weather app. it still doesn’t load after 5 minutes so I think somethine’s wrong. I thought my balance was too low and refilled it. now I have 57euro in the balance and still doesn’t work

I already did the Live-Check and there is no trouble in my area. 

What’s happening and is there anything you can do about it?

Thanks