In the same way that we are all seeing increases in the cost of living, insurance companies will also be seeing their costs increase in relation to claims and vehicle repair costs and we all contribute to these increased costs whether we have claim or not. The Association of British Insurers article at the link below summarises some of the increases affecting claims costs that feed through into the premiums we pay;
https://www.abi.org.uk/news/news-articles/2023/2/rising-cost-pressures-push-up-the-price-of-motor-insurance/You’ve said your premium has increased for no reason - there will be reason(s), although they may not necessary be directly related to you personally as an insurance risk. It could be that your insurance company has seen a significant increase in the number and cost of claims overall for mk7.5 Golf GTI pp’s overall as a risk segment. If so, then premiums for all policyholders in that risk segment are likely to increase. My premium also increased this year; by around 15%. For me as an insurance risk, nothing has changed compared to last year so I could also say my premium has increased for no reason.
Car insurance is seen by many as a grudge purchase as the majority of people see nothing in return for the premium they pay. As always, if you feel your premium increase is excessive, then shop around to see if you can get a better price. However, don’t necessarily go for the cheapest price - it might be cheapest for a reason; e.g. poor claims service, poor customer service, lower levels of cover. If practical to do so, you could also consider making changes to your insurance that might reduce the cost - e.g. pay your premium annually if you can afford to as it works out cheaper than paying monthly, increase your excess, limit the annual mileage you drive if you can legitimately do so, review any add-ons you have on your policy and consider deleting any if they’re no longer required.