I turn to Allah Exalted in repentance from all sins, but immediately after repenting, I may do a disliked act—not necessarily a forbidden one. Thereupon, I feel that I have ruined my repentance and therefore renew it and resolve not to commit this sin ever again and say that if I did, I would give 500 riyals in charity as a deterrent. Nevertheless, few minutes later, I would recommit it and, as a consequence, I intend to recite thikr (remembrance of Allah) one thousand times if I ever commit that sin again, but I keep committing it! The total number of thikr that I have vowed to recite amounts to 300,000. What should I do about the vowed money and thikr? Should I fulfill those vows or what should I do?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

If you have uttered the very words that you mentioned in your question, then this is just a promise. The majority of the scholars believe that one is not obliged to deliver on his promise. However, if the formula that you have pronounced suggests commitment, such as by saying, 'I commit myself to do such-and-such act', or any statement that bears the same indication, then it is considered a vow. Such a vow, in this context, is known as a vow of lajaaj (i.e. anger). We have underlined the religious ruling on the vow of lajaaj in detail in many Fataawa.

In conclusion, you should do what you had vowed to do or offer an expiation like that for breaking an oath for each vow you had taken and failed to fulfill. You have the choice to do any of these two options.

As for the sins that you commit, you should turn to Allaah, the Exalted, in sincere repentance and carry out as many righteous deeds and voluntary acts of worship as you can so as to draw you closer to Allaah, the Exalted. Repentance wipes out sins and misdeeds. You should avoid disliked acts to the best of your ability. Although doing disliked acts does not constitute a sin, abandoning them out of hope for earning the pleasure of Allaah, the Exalted, is something for which the person earns a reward. 

Allaah Knows best.