Please don't pay them whatever you do. I presume they called you out of the blue (cold-called you)?.
What has happened is StratX run a scam - I have checked and that trading company is not authorised according to the Financial Conduct Authority (the FCA). The law changed in 2020 and if they are to take your money as a UK citizen they must be authorised - to not obtain authorisation means they have acted illegally. They then sold your details to another scam company to try and get more money out of you. A red flag is being asked to pay a large up front sum.
The first thing to do is to report this to the Police and to Action Fraud so that you can obtain a crime reference number. The Action Fraud website where you can report the crime is here: https://www.actionfraud.police.uk/
Once you have done that then see if your bank or credit card company can do a charge-back on the monies as a lot of these trading companies are not legitimate outfits. If you paid with a credit card you may be able to make a claim against the card provider under Section 75 of the Consumer Credit Act. If you paid by debit card then your bank may be subscribed to the consumer voluntary code to refund you if you have been scammed. The bank can charge-back up to 120 days from the date you sent money or paid money to a scammer, or from the date you first noticed the problem.
In future my advice is to check whether the trading company is FCA-regulated first of all to ensure they are legitimate. You can check here : https://register.fca.org.uk
The FCA website has a list of regulated companies so this would be worth checking. If you prefer to speak to the FCA then they can be reached on 0800(###) ###-####
If there is no record, I would urge caution and do not give them your personal details, nor any money. The reason being if they are unregulated, there is nothing the FCA can do and in all likelihood the company is based abroad so suing them would be difficult if you wanted your money back. Most of these companies also ask for the initial £250 up front and tempt you to add more funds only for them to become non-responsive when you ask to withdraw.
There are a few companies who can claim to retrieve monies taken by a scammer but in reality they are also scams - the first scammer sells your data to another scammer. Once a scammer has the money it would be very difficult to sue them (most of them being based abroad) and even if you obtained a CCJ against them, enforcing it is another matter.
You can try any of these regulated law firms to see if they can recover the money for you:
They should be able to help you with a no win no fee agreement so that you do not have to pay anything up front to them. These are regulated law firms in the UK.