As @papso22 has already pointed out, you will need to contact eBay Customer Services to see if they will do that for you. However, in case you are unfamiliar with how to contact eBay Customer Services I have included the link here https://www.ebay.co.uk/help/eua?id=5275&mkevt=1&mkpid. Click on that link and a new page will appear on the screen. Scroll right down to the bottom of the page and you will see a blue button with the words "Have Us Call You" on it. Although you can click on that button at any time betweeen 8:00am and 10:00pm from Monday to Friday or 9:00am and 6:00pm on Saturday and Sunday, the best option would be to click on the button to request a call from eBay just after the lines open first thing in the morning, as if you do that you stand a far greater chance of getting a call back from one of eBay's more knowledgeable representatives based in Dublin, whereas if you were to leave it until much later in the day you may well get a call back from an eBay representative working out of eBay's Philippines-based call centre, which could result in a phone call with somebody whose command of the English language leaves a lot to be desired!
If you do decide to take this advice then once you get a call back from an eBay representative explain what has gone wrong, but make sure that you emphasise to whoever you are speaking to that you were not trying to set up an off-eBay deal, as it is more than likely that eBay suspected that that is exactly what you were attempting to do, hence the reason why eBay have blocked your messages.
If you can convince eBay that this really was nothing more than a genuine mistake on your part then they may well relinquish the blocks on your messages, although you will have to be very careful from now on that you do not make the same mistake again, as eBay will no doubt be watching your account like a hawk for a while afterwards so as to satisfy themselves that this was indeed a one-off slip-up, as opposed to a thwarted attempt at setting up an off-eBay sale.
