Divorce in Islam is actually quite complicated. Many hadiths say one thing while other says something else, esp. regarding triple divorce (three divorces uttered at once). Some say they count as one divorce. They say this was the rule during Prophet Muhammad last era as well Abu Bakr and Umar (RA) era. In short this was a problem among Muslims. Umar (RA) was strictly against triple divorce. For the right reason that triple divorce ends the marriage altogether and ends any reconciliation efforts between the couple. There is simply no taking back. That's probably the reason they reformed it so that triple divorces counts as single divorce.
Some Clarification about Talaq
Recommend way of Talaq is, one occurrence at a time. Then one has to wait for the women Iddath period. If the husband reconciled with his wife and want to take her back, he can! His wife will does not count. He can do so by having sexual intercourse with her or may be some foreplay. No need to remarry her again or bring any witnesses!
If the period of iddath (usually three months) has passed, he has to offer her marriage proposal again and she may accept/reject. A new mahar will be decided in this case and the marriage has to be proper. This is true in case of one or two divorces.
If three divorces have taken place, the man cannot take his wife back, although some say he still can within her Iddath period.
Your Particular Case
Divorce has taken place when he issued it during menses. This divorce counts. Let me be on reformed version. That divorce counts as one divorce.
Divorce agains took place when you heard about it from your relative (reliable witness). Although he said it thrice, let’s count it as second divorce only.
Divorce took place for the third time when he sent you divorce papers. That means all three divorces have taken place. Reference
Going back to your previous husband
It is not permissible to remarry your ex-husband unless you have married someone else. Your second marriage must be a valid marriage and NOT for the purpose of halala. Your second husband must divorce you with his own free will in order for you to marry your first husband. If it is already been decided, he will consummate and divorce you, it is counted as sin.
My personnel View
I by no means am trying to stop you from marrying your ex-husband because of religion reasons. May be there is a point that you have left in the question that an Aalim can take advantage of and will allow you to re-marry him. Perhaps you can talk to a local Imam for that matter. I wish you all the best!