Who are they going to ask for help? How? What's in it for the possible helpers? The Vikings raided everywhere possible. From Iceland (which they colonized) to the Black Sea. The holy Roman empire didn't exist as yet. France didn't exist as yet. The German emperor did exist, but he was not very strong and had plenty of problems to solve already. Besides, he didn't have a navy.
The Frankish king (something very different from the king of France) basically lost out and had to give away the area that became the duchy of Normandy to the Vikings. He couldn't help, even if he had wanted.
Supposing the Frankish king had the wherewithal to assist British kings (plural, there were several kingdoms), he would have been William the Conqueror a few centuries earlier. An opportunity like that is something no king can resist.
Given the fact that the French king has to eat humble pie (with extra slices and a cherry on top) by giving away Normandy, he wasn't in any position to offer help, even if he wanted. Just like the German emperor, he had a lot of other things to worry about.
Now, about the Emirate of Cordoba, that did exist (sorry, I thought it came into existence later). But that emirate was itself a conquest by muslims of Christian Spain. Why would a Christian king of England ask for support from a) heathens* and b) heathens that conquer and subjugate?
heathens* = until very recently Christians saw muslims at best as believers in a different (wrong) god, and more often a a good deal worse.
What you did was looking at history with our modern views. That never works.