Allah's saying:

وَلَقَدْ أَخَذْنَاهُم بِالْعَذَابِ ...

And indeed We seized them with punishment,

means, `We tried and tested them with difficulties and calamities.'

His saying:

... فَمَا اسْتَكَانُوا لِرَبِّهِمْ وَمَا يَتَضَرَّعُونَ ﴿٧٦﴾

but they humbled not themselves to their Lord, nor did they invoke with submission to Him.

means, that did not deter them from their disbelief and resistance, rather they persisted in their sin and misguidance,

فَمَا اسْتَكَانُوا (but they humbled not themselves),

وَمَا يَتَضَرَّعُونَ (nor did they invoke (Allah) with submission to Him).

they did not call on Him.

This is like the Ayah:

فَلَوْلا إِذْ جَآءَهُمْ بَأْسُنَا تَضَرَّعُواْ وَلَـكِن قَسَتْ قُلُوبُهُمْ

When Our torment reached them, why then did they not humble themselves! But their hearts became hardened, (6:43)

Ibn Abi Hatim recorded that Ibn Abbas said,

"Abu Sufyan came to the Messenger of Allah and said, `O Muhammad, I ask you by Allah and by the ties of kinship between us, we have been reduced to eating camel hair and blood.'

Then Allah revealed, وَلَقَدْ أَخَذْنَاهُم بِالْعَذَابِ فَمَا اسْتَكَانُوا (And indeed We seized them with punishment, but they humbled not themselves).

This was also recorded by An-Nasa'i.

The basis of this Hadith is in the Two Sahihs, where it says that the Messenger of Allah prayed against the Quraysh when he could not make any headway with them, and he said,

اللَّهُمَّ أَعِنِّي عَلَيْهِمْ بِسَبْعٍ كَسَبْعِ يُوسُف

O Allah, help me against them sending on them seven years (of famine) like the seven (years of drought) of Yusuf.