@MM we all know Trump is a big liar, and those who don't, can just google 'Trump contradicts himself' and watch one of the many videos that appear.
Sadly, however, I can confirm that mex. president is liar too, and in any case, if we can be sure of something is that if he discussed the wall payment at all, he did in the most incompetent way possible.
Anyway, there are strong resons why his governmet just won't pay a cent (at least soon):
1. Basically, no mony
2. 2018 mexican elections. PRI paying a cent for the wall, would be a political suicide
New president would enter december 2018. By then, if Trump wins and he keeps serious about that bullshit, the political and economical crisis in Mexico might be BIG, so things wouldn't be so easy to predict. But most probably Trump crisis would appear in the US too.