As you have discovered, periwinkle (Vinca major) is a nuisance to deal with. A possible explanation for the failure of the two herbicides you used is that periwinkle leaves are covered with a waxy- like substance, called a cuticle, that repels water.Triclopyr amine ("Brush B Gone") can be mixed per label instructions and then a small amount of mineral oil or other non-ionic substance can be added. Triclopyr is a selective broadleaf herbicide, so any grasses will not be impacted, but other shrubs and trees should be protected from the spray. Follow the label instructions carefully, especially heeding the protective gear to be used for skin and eyes. Spraying should be done in early spring when leaves first emerge.

Most sources regard manual removal as a better alternative to herbicides. Since periwinkle roots along its stems, as well as roots from the smallest part of stem left in the ground, it is a multi-year process for complete removal. Rake the plants to loosen them from the soil, then pull or cut them. Place all pieces in a plastic bag and remove it from the property. Do not compost it! As new plants emerge, remove them immediately. A complete description of this process can be found at www.nps.gov/plants/alien/pubs/ Search for "control vines". While some other sources suggest mowing the plants repeatedly, the tendency for any small remnant to root makes this somewhat self-defeating. Good luck in getting rid of this pest.