Thank you. There is actually no such thing as a credit rating as such. Rather each person has a "credit history" which is recorded with credit reference agencies of which there are three. There will be some commonality between the information held by credit reference agencies but it will not be identicaly because it will depend with which institutions each agency has relationships. If you have been out of the country for the last 6 years or more it may be that the agencies will have little or no information about you.
What companies do when they apply for a credit check is apply for information about you from the credit agencies - this will include accounts you hold including payment histories, any default notices, whether you are registered to vote and so on. They will feed this into their own private credit model which they use to determine the kind of applicant they are looking for for their product and make a decision. Different companies will look for different applicants. Most mainstream lenders will look for people who have a good history of repayments on time but some companies, e.g. conpanies that offer products for poor credit may actively want people with chequered histories sothey ca charge late payment fees. As a result this is why I say there is no such thing as a bad credit rating or no credit rating because each company sets their own way to score.
What is quite possible is that you are strugling to obtain credit because there is little information about any past credit for you. It could also be that there is some incorrect information recorded about you but that is hopefully unlikely.
The first step would be to apply for copies of your credit files. There are two services that you can use to gain access to your Callcredit and Equifax files for free. These are called "noddle" and "clearscore". There are no monthly charges for their free services and they will give you a monthly credit report for free. If you find there is little or no information about you this is likely your issue and you will need to consider building a credit profile for yourself.
You can start by ensuring you are registered to vote. Not being regitered is a big negative even if you otherwise have good credit. Next consider ensuring you have at least one bank account registered in your names and your address. Next consider applying for a credit product. If you have little or no credit history consider a credit card which offers for poorer credit scores. There is quite a useful tool you can consider using here to find cards that you are likely to be accepted for:
Use the card for some purchases for a few months and set up a direct debit to make the monthly repayments. The last thing you would want to do is have missed payments recorded on any fledgling credit report history. After a few months your credit file will build a history and you will increasingly have more normal access to credit. The above services use algorithms to generate a specimin credit score for you as part of their service. As above this is not your "credit rating" as this does not exist but it will show you how each agency considers your credit and you can see as it improves. Dye to the above, you will notice your score will almost certainly be different between the two services - this is as a result of the above, but it will still be a useful tool or guide for you to see how your credit profile is improving.
In terms of accessing essential services now, like broadband, many companies will offer you the products even with a lack of credit history but may ask you to pay a deposit for the account for say 6 or 12 months until you build up a better history. If the current broadband provider doesn't offer this there are many that do.
Does the above answer all your questions? If it does, I should be very grateful if you would kindly take a moment to click a rating for my service to you today. Your feedback is important to me. If there is anything else I can help with please reply back to me though