Think you need a bit more patience there. No point Spraying for a fortnight you need to spray roundup onto green shoots so once every 2-3 weeks and if it's deep or cut/rotavated then it may take 2 years to be sure it has all germinated and been killed.I am just about to returf my lawn of about 70SqM because of couch grass.
My plan is spray with glyphosate (Doff weed killer) then keep spraying for the next fortnight to ensure everything is dead.
Then a turf cutter to remove the old grass and also to drop the whole lawn by about an inch.
Then rotovate and level and put new turf down.
I’ve tried all sorts to try and get rid of it, but to no avail. As soon as I dig out a patch another bigger one appears somewhere else. Raking the lawn prior to mowing to make it stand upright was a complete waste of time. I’ve tried to ignore it, but once I’ve seen it, I can’t unsee it and finally decided to get rid of it all and start again.