I hope it's not too late to help.

I too had trouble a few years ago crediting my flights. I did it online and and the miles instantly appeared in the account.

After logging into Avianca Plus, click on "acumule o utilice sus Millas" > directly under it, click on Nombre en Ingles.

Here, for each segment you flew, you would choose the origin and desination, date, airline (Avianca or Sam), if you have your ticket number (yes or no). If you have the ticket number, enter it in the next field. If you choose no, enter the flight number and your seat number (number and then letter).

I don't have any to try to make sure it still works, but like I said, it worked immediately a few years ago.

Good luck!