Matadi is probably the best place for you now
We had an absolute nightmare with the Angolans... for reasons I would pay good money to see someone comprehend... I have no idea!
Looooooong story short we had a single entry 30-day visa which we had to use to get through Cabinda (Nooooo!) so we basically used our gold-dust 30-day visa for 1 hour!
We then managed to get into DRC by telling the border officials that our single-entry 30-day visa was valid for a 2nd entry, into Angola mainland. We only had a transit visa for DRC. They bought it, but of course we weren't able to enter Angola proper. Arriving in Matadi we were able to obtain a 5-day transit visa for Angola the same day. Of all the Angolan consulates we went to (Abuja, Pointe-Noire, Brazzaville, Matadi) they were by far and away the friendliest and most helpful. All kudos to them, and if you can, don't even bother with the others - they are all about as unhelpful as you can imagine.
Of course the only possible sticking point you will have will be to gain entry to the DRC in order to get to the Angolan consulate in Matadi. They are notorious for turning people back if you don't have onward travel plans.
Hope this helps