Is my work at a technical support company, where solutions to technical problems were delayed and I would send urgent requests without knowing the reason for the delay, considered a sin, and how can I expiate it?

What you have mentioned does not incur sin. The basic principle is the innocence of the technician until his negligence is proven, and accusing him of negligence without clear evidence is an injustice. If he was negligent and this was not clear to you, then the sin is upon him and there is nothing upon you. In the event that his negligence becomes clear, it is permissible to rebuke him and inform the authorities, provided that no harm results to you from doing so.