He did not fast Ramadan and he thought negatively of Allah, may He be exalted

Firstly: 

We ask Allah, may He be exalted, to accept your repentance,
forgive you your sins, open your heart to faith and guidance, and to keep
away from your mind all negative thoughts of your Lord and Creator, for
there is nothing stranger than a person thinking negatively of his Lord when
He has blessed him and bestowed upon him thousands of blessings, the
greatest of which are the blessing of Islam and the blessing of reason. For
He has chosen him from among His creation and has not made him a
disbeliever; He has blessed him by making him a human who thinks rationally
and ponders things, unlike animals and those who are insane. And He has
created in his body and soul blessings of which no one knows the number
except Allah. 

One of Allah’s blessings is that He tests His slave with some
calamities in order to expiate some of his bad deeds, or to increase him in
status, or to remind him that he will return to Him and stand before Him.
How often has a person turned away from Allah, then calamity was the means
that caused him to turn back to Allah and repent, and ultimately turned out
to be a means that led to happiness and joy. 

When a person is certain that Allah, may He be exalted, is
more merciful to him than anyone else, he will be content with His decree,
will bear with patience that with which He tests him, and will hope for
relief granted by Him. 

Think about the blessings that Allah has bestowed upon you;
this will increase your gratitude towards Him and will make you recognise
His bounty. Remember that no calamity befalls you but there is something
good for you in it. 

The Prophet (blessings and peace of Allah be upon him) said:
“No exhaustion, sickness, worry, grief, harm or distress befalls a believer,
not even a thorn that pricks him, but Allah will expiate some of his bad
deeds thereby.”

Narrated by al-Bukhaari, 5642; Muslim, 2573 

At-Tirmidhi (2399) narrated that Abu Hurayrah (may Allah be
pleased with him) said: The Messenger of Allah (blessings and peace of Allah
be upon him) said: “Calamities will continue to befall the believing man or
woman affecting himself or his child or his wealth, until he will meet Allah
with no sin on him.” 

At-Tirmidhi (2398) and Ibn Maajah (4023) narrated that Sa‘d
ibn Abi Waqqaas (may Allah be pleased with him) said: I said: O Messenger of
Allaah, which people are most severely tested? He said: “The Prophets, then
the next best and the next best. A person is tested according to his
religious commitment. If he is steadfast in his religious commitment, he
will be tested more severely, and if he is shaky in his religious
commitment, his test will be according to his commitment. Trials will
continue to afflict a person until they leave him walking on the earth with
no sin on him.”

Classed as saheeh by al-Albaani in Saheeh at-Tirmidhi. 

Secondly: 

If a person feels resentment towards Allah, may He be
exalted, in his heart, or is angry with His decree or thinks negatively of
Him – Allah forbid – then let him renew his Islam and utter the
Shahaadatayn (twin declaration of faith), and let him strive hard and do
righteous deeds. 

He does not have to make up the fasts that he deliberately
omitted, because that is an act of worship that is connected to a specific
time; if a person deliberately omitted it at the time it was due, it would
not be accepted from him after that. Moreover, Islam erases what came before
it of sins. 

Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) was
asked: What is the ruling on the Muslim who for many years did not fast
Ramadan, even though he did some of the other obligatory duties, and he had
no impediment that was keeping him from fasting? Does he have to make up the
fasts if he repents? 

He replied: 

The correct view is that he does not have to make up the
fasts if he repents, because in the case of every act of worship that is
connected to a specific time, if a person deliberately delays it without an
excuse, then Allah will not accept it from him. 

Based on that, there is no benefit in making it up. But he
has to repent to Allah, may He be glorified and exalted, and do a lot of
righteous deeds. And whoever repents, Allah will turn to him in mercy.

End quote from Majmoo‘ Fataawa ash-Shaykh Ibn ‘Uthaymeen,
19/87 

We ask Allah to increase you in faith and guidance. 

And Allah knows best.