Ja Rule is currently scrambling trying to figure out why his UK Tour fell apart days before it was supposed to jump off — and now he has to fend off 50 Cent once again!!!

On Tuesday, Ja offered ticket holders of his UK Tour a refund with a heavy heart after accepting the bad news.

Apparently, Ja’s past criminal record caught up to him all the way in the UK, where officials made it clear there would be no “Venni Vetti Vecci” going down in that country, as they barred him from entry.

Despite his claims that 85% of the shows were sold out, Ja says he’s now out $500k of his own pocket and the tour ain’t happening!!!

His announcement was interesting … Ja made the news public on Monday but fans have been getting notifications for days now, and none of his tour mates Keri Hilson, Mya or Lloyd have been promoting the show on their social media.

Maybe Ja was trying to hold out for some sort of British miracle?!?

Ja’s bad fortune multiplied when 50 Cent entered the chat after fans blamed him for somehow masterminding the “Iconn” rapper’s UK ban.

50 swore off the negativity as a New Year’s resolution, but couldn’t help but get in a couple of digs … calling Ja a “bitch” and reminding him that his own ‘Final Lap’ tour had ZERO issues in the UK!!!

Ja didn’t take 50’s jabs lying down, and cracked back with a couple short, but bitter retorts — but he’s still tour-less for the time being. Soooo … not exactly a great last laugh.