After I replaced the front lower control arm I could not fasten the front bolt into the sub frame, because there were not threads / nut in the sub frame, they were just missing.

Q , has anyone had this probem before and any sugestions how to fix it?

Can't remember the exact subframe on a MK4 but the safest way is to replace the subframe.

There's generally a nut tacked inside, the tack breaks and the nut falls off.
If space allows, A quick fix would be to drill a hole at the bottom and fit a nut in. I seen a few cars that were done like this.

Whether it weakens the frame, I'm not sure. I don't think a +-19mm hole would weaken it much if any.

Sent from my CPH2371 using Tapatalk

Many thanks for your answer, I have made a slot and inserted a steel bar 20 mm x 8 mm 38 mm long and I am very satisfied with the repair